GB2262836A - Optical pre-amplifier/receiver arrangement. - Google Patents

Optical pre-amplifier/receiver arrangement. Download PDF

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Publication number
GB2262836A
GB2262836A GB9127402A GB9127402A GB2262836A GB 2262836 A GB2262836 A GB 2262836A GB 9127402 A GB9127402 A GB 9127402A GB 9127402 A GB9127402 A GB 9127402A GB 2262836 A GB2262836 A GB 2262836A
Authority
GB
Grant status
Application
Patent type
Prior art keywords
amplifier
optical
pre
receiver
receiver arrangement
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Withdrawn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
GB9127402A
Other versions
GB9127402D0 (en )
Inventor
Robert Anthony Baker
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
Nortel Networks 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

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Classifications

    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B10/00Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/60Receivers
    • H04B10/66Non-coherent receivers, e.g. using direct detection
    • H04B10/67Optical arrangements in the receiver
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01SDEVICES USING STIMULATED EMISSION
    • H01S3/00Lasers, i.e. devices for generation, amplification, modulation, demodulation, or frequency-changing, using stimulated emission, of infra-red, visible, or ultra-violet waves
    • H01S3/10Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/13Stabilisation of laser output parameters, e.g. frequency, amplitude
    • H01S3/1301Stabilisation of laser output parameters, e.g. frequency, amplitude in optical amplifiers
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B10/00Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/60Receivers
    • H04B10/66Non-coherent receivers, e.g. using direct detection
    • H04B10/67Optical arrangements in the receiver
    • H04B10/671Optical arrangements in the receiver for controlling the input optical signal
    • H04B10/672Optical arrangements in the receiver for controlling the input optical signal for controlling the power of the input optical signal
    • H04B10/673Optical arrangements in the receiver for controlling the input optical signal for controlling the power of the input optical signal using an optical preamplifier
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01SDEVICES USING STIMULATED EMISSION
    • H01S3/00Lasers, i.e. devices for generation, amplification, modulation, demodulation, or frequency-changing, using stimulated emission, of infra-red, visible, or ultra-violet waves
    • H01S3/05Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06Construction or shape of active medium
    • H01S3/063Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
    • H01S3/067Fibre lasers
    • H01S3/06754Fibre amplifiers

Abstract

An optical pre-amplifier/receiver arrangement for an optical fibre telecommunications system wherein the pre-amplifier (11) is an optical amplifier having an automatic gain control (16) whereby the optical output of the pre-amplifier applied to the receiver input is maintained constant. <IMAGE>

Description

Optical pre-amplifier/receiver arrangement This invention relates to an optical pre-amplifier/receiver arrangement for use in long haul optical fibre systems, for example submarine systems.

An optical pre-amplifier can be used to enhance the sensitivity of a conventional receiver. Sensitivities at least as low as -39.5 dBm have been achieved by the applicants at 2.5 Gbit/s, and lower still have been reported elsewhere, which are similar to those being achieved using coherent receivers.

A significant drawback to optically pre-amplified receivers is that when operated in the constant gain mode the dynamic range of the combination is reduced, compared to that of the receiver alone. This is because, to operate at maximum sensitivity, the optical amplifier has to be the dominant noise source in the system, and therefore is operated at high gain.

The situation is depicted in Figure l(a) and l(b). Here sensitivity of the pre-amplifier/receiver combination is plotted vs amplifier gain and, as seen to achieve maximum sensitivity, gains of 30 dB may be required. Figure l(b) shows the received light level at the receiver photodiode itself, and it is observed that levels as high as -15 dBm may be required to achieve maximum sensitivity.

In a real system, it would be normal practice to install the receiver/pre-amplifier optimised for maximum sensitivity.

However, in this case, because allowances for repair and ageing have not been used up, the signal level at the receiver itself could be 10 dB higher than that end of life, and as a consequence the receiver would overload (Figure 2).

According to the present invention there is provided an optical pre-amplifier/receiver arrangement for an optical fibre telecommunications system wherein the pre-amplifier is an optical amplifier having an automatic gain control whereby the optical output of the pre-amplifier applied to the receiver input is maintained constant.

A preferred embodiment of the invention will now be described with reference to the accompanying drawings, in which: Figures l(a) and l(b) respectively illustrate sensitivity of pre-amplifier/receiver vs amplifier gain and signal level at receiver input vs sensitivity of pre-amplifier/receiver; Figure 2 illustrates operating signal level at an optical receiver photodetector at the start of system life; Figure 3 illustrates schematically an optical pre-amplifier/receiver arrangement, and Figure 4 illustrates sensitivity of optical pre-amplifier/receiver combination vs amplifier gain with effective input level tracked by automatic gain control.

The invention seeks to provide an optical pre-amplifier/receiver arrangement which adjusts amplifier gains so as to maintain adequate sensitivity for the system lifetime. The preferred arrangement is shown in Figure 3. An incoming optical fibre 10 is coupled to an optical amplifier 11 the output of which is applied, via an optical bandpass filter 12, to a receiver 13.

Between the filter 12 and the receiver 13 there is incorporated an optical coupler 14 which taps off a small portion of the optical signal applied to the receiver. Typically the coupler may be a 10:1 skew coupler. The tapped off signal is fed to a monitor photodiode 15 to provide a feedback signal to an automatic gain control (AGC) circuit 16 which controls the gain of the amplifier 11. For longhaul optical fibre systems such as submarine systems it is convenient to use optical amplifiers in which a length of amplifying fibre is pumped by a local laser. Typically the amplifying fibre is an erbium doped fibre. Provision of AGC for an erbium doped optical amplifier is already known from our copending application No. 89 09222.5 (Serial No. 2230912).

The mean power at the monitor photodiode 15 will be a measure of the signal level at the output of the pre-amplifier. The gain of the pre-amplifier is adjusted during the life of the system to maintain a constant level at the monitor photodiode, and thereby a wide dynamic range can be realised from the preamplifier/receiver combination as a whole.

The AGC loop is set up to deliver the required sensitivity at minimum input level. At higher input levels the gain is reduced by the AGC. Whilst this does degrade the sensitivity of the receiver/pre-amplifier combination, this is more than offset by the higher signal level at the pre-amplifier input. Indication of the safety margin associated with AGC is shown in Figure 4. A dynamic range in excess of 20 dB can be achieved by this technique.

Claims (6)

CLAIMS:
1. An optical preamplifier/receiver arrangement for an optical fibre telecommunications system wherein the pre-amplifier is an optical amplifier having an automatic gain control whereby the optical output of the pre-amplifier applied to the receiver input is maintained constant.
2. An optical pre-amplifier/receiver arrangement according to claim 1 wherein the optical amplifier comprises a pumped erbium fibre amplifier with feedback AGC.
3. An optical preamplifier/receiver arrangement according to claim 2 wherein the feedback AGC controls the pump power applied to the erbium amplifier.
4. An optical pre-amplifier/receiver arrangement substantially as described with reference to the drawings.
5. A method of optimising sensitivity of an optical pre-amplifier/receiver arrangement including providing feedback automatic gain control for the optical pre-amplifier.
6. A method according to claim 5 wherein the optical pre-amplifier is a pumped erbium fibre amplifier, the feedback AGC being effective to adjust the pump power applied to the erbium fibre to maintain the amplifier output constant.
GB9127402A 1991-12-24 1991-12-24 Optical pre-amplifier/receiver arrangement Withdrawn GB9127402D0 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB9127402A GB9127402D0 (en) 1991-12-24 1991-12-24 Optical pre-amplifier/receiver arrangement

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
GB9127402A GB9127402D0 (en) 1991-12-24 1991-12-24 Optical pre-amplifier/receiver arrangement
FR9215623A FR2687867A1 (en) 1991-12-24 1992-12-23 Assembly preamplifier and optical receiver, and method of optimizing its sensitivity.
JP34490092A JPH0697891A (en) 1991-12-24 1992-12-24 Optical preamplifier and receiver

Publications (2)

Publication Number Publication Date
GB9127402D0 GB9127402D0 (en) 1992-02-19
GB2262836A true true GB2262836A (en) 1993-06-30

Family

ID=10706832

Family Applications (1)

Application Number Title Priority Date Filing Date
GB9127402A Withdrawn GB9127402D0 (en) 1991-12-24 1991-12-24 Optical pre-amplifier/receiver arrangement

Country Status (3)

Country Link
JP (1) JPH0697891A (en)
FR (1) FR2687867A1 (en)
GB (1) GB9127402D0 (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2750552A1 (en) * 1996-06-26 1998-01-02 Alcatel Submarcom Receiver for digital signal transmission system optically
EP0971464A2 (en) * 1998-07-10 2000-01-12 Ando Electric Co., Ltd. Optical pulse generator

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4886334A (en) * 1987-09-01 1989-12-12 Nec Corporation Optical amplifying repeater
US4954786A (en) * 1989-01-12 1990-09-04 Kabushiki Kaisha Toshiba Optical amplifying device
GB2230912A (en) * 1989-04-22 1990-10-31 Stc Plc Optical amplifier gain control
US5050949A (en) * 1990-06-22 1991-09-24 At&T Bell Laboratories Multi-stage optical fiber amplifier
GB2244595A (en) * 1990-04-18 1991-12-04 British Telecomm Optical fibre amplifier with automatic gain control

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4886334A (en) * 1987-09-01 1989-12-12 Nec Corporation Optical amplifying repeater
US4954786A (en) * 1989-01-12 1990-09-04 Kabushiki Kaisha Toshiba Optical amplifying device
GB2230912A (en) * 1989-04-22 1990-10-31 Stc Plc Optical amplifier gain control
GB2244595A (en) * 1990-04-18 1991-12-04 British Telecomm Optical fibre amplifier with automatic gain control
US5050949A (en) * 1990-06-22 1991-09-24 At&T Bell Laboratories Multi-stage optical fiber amplifier

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2750552A1 (en) * 1996-06-26 1998-01-02 Alcatel Submarcom Receiver for digital signal transmission system optically
EP0817408A1 (en) * 1996-06-26 1998-01-07 Alcatel Submarine Networks Receiver for optical digital signal transmission system
US5854704A (en) * 1996-06-26 1998-12-29 Alcatel Submarine Networks Receiver for optical digital transmission system
EP0971464A2 (en) * 1998-07-10 2000-01-12 Ando Electric Co., Ltd. Optical pulse generator
EP0971464A3 (en) * 1998-07-10 2001-09-12 Ando Electric Co., Ltd. Optical pulse generator

Also Published As

Publication number Publication date Type
GB9127402D0 (en) 1992-02-19 grant
JPH0697891A (en) 1994-04-08 application
FR2687867A1 (en) 1993-08-27 application

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Legal Events

Date Code Title Description
WAP Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1)