GB2326996A - Optical fibre amplifier with absorption medium to reduce noise - Google Patents
Optical fibre amplifier with absorption medium to reduce noise Download PDFInfo
- Publication number
- GB2326996A GB2326996A GB9813874A GB9813874A GB2326996A GB 2326996 A GB2326996 A GB 2326996A GB 9813874 A GB9813874 A GB 9813874A GB 9813874 A GB9813874 A GB 9813874A GB 2326996 A GB2326996 A GB 2326996A
- Authority
- GB
- United Kingdom
- Prior art keywords
- optical fiber
- light
- medium
- pump
- signal
- 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- Withdrawn
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
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/29—Repeaters
- H04B10/291—Repeaters in which processing or amplification is carried out without conversion of the main signal from optical form
- H04B10/2912—Repeaters in which processing or amplification is carried out without conversion of the main signal from optical form characterised by the medium used for amplification or processing
-
- 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
- H01S3/06758—Tandem 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
-
- 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
-
- 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
- H01S3/10007—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating in optical amplifiers
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/29—Repeaters
- H04B10/291—Repeaters in which processing or amplification is carried out without conversion of the main signal from optical form
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B2210/00—Indexing scheme relating to optical transmission systems
- H04B2210/003—Devices including multiple stages, e.g., multi-stage optical amplifiers or dispersion compensators
Description
OPTICAL FIBER AMPLIFIER HAVING LOW NOISE
BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to an optical fiber amplifier1 and more particularly, to an optical fiber amplifier having low noise, which reduces noise regardless of the size of an input light signal.
2. Description of the Related Art
In a general repeater for long distance communications, a conventional optical communications repeating method is performed in a manner such that a weakened light signal is transformed temporarily into an electrical signal for amplification, and the amplified electrical signal is transformed back into an optical signal. Such a repeating method excessively increases the size of a repeating amplifier system and increases noise. An optical fiber amplifier for amplifying an optical signal is required as a repeater to overcome the above problem and effectively amplify an optical signal.
An erbium doped fiber amplifier (EDFA), being such a fiber amplification repeater, is attracting attention as a next-generation optical repeater for optical communications. The EDFA periodically amplifies an optical signal to prevent attenuation of the optical signal due to long distance transmission, when much data is transmitted over a long distance via an optical fiber.
FIG. 1 is a block diagram showing the configuration of a normal single forward EDFA comprising an erbium doped fiber (EDF) 130 being an optical signal amplifying medium, a pump laser diode (LD) 120, a wavelength division multiplexer (WDM) 110, and isolators 100 and 140. Here, the pump LD 120 functions as a light source for exciting erbium ion of a ground state in the EDF 130. The WDM 110 couples lights with different wavelengths and transmits the result to a single line. The isolators 100 and 140 prevent an optical signal from proceeding backward.
The WDM 110 couples a signal light and a pump light into a fiber and transmits the fiber to the EDF 130. The optical isolator 100 before the WDM 110 prevents amplified spontaneous emission (ASE) generated by the EDF 130 from proceeding to an input port. Similarly, after the EDF 130, the isolator 140 prevents the amplification efficiency of the EDFA from being degraded due to ASE and a amplified light signal which are reflected by an optical device such as a signal output connector and reenters the EDF 130.
Meanwhile, gain and signal-to-noise ratio (SNR) are the most important properties of an optical amplifier. These factors are linked to the intensity of the light signal input to the optical amplifier. A noise figure can be expressed by
Equation 1, and gain can be expressed by Equation 2: N.F. = PASE ...(1)
GMiAv
G = Pout-Pin ...(2)
Pin In Equation 1, N.F. denotes noise figure, i.e., noise, PASTE denotes the ASE power level, h is Plank's constant, and v is the frequency. In Equation 2, G indicates gain, Pout indicates the output of an optical amplifier, and p indicates the intensity of a light signal input to the optical fiber amplifier. A graph of the input signal-to-gain of the normal optical fiber amplifier is shown in FIGS. 2 and 3.
As shown in FIGS. 2 and 3, when the signal light is small, gain is constant and PASE acting as noise level increases. When the signal light is large, PASE is constant and gain decreases. Accordingly, if the Equations 1 and 2 are applied, since the gain is constant and PASTE increases when the signal light is small, the
SNR is large. On the other hand, since PASE is constant and gain decreases when the signal light is large, the SNR is increased.
That is, when a signal light, amplified with a lot of noise generated when the input of the signal light is small or large, is transmitted to a receiver via an optical fiber, reception sensitivity is deteriorated. When optical fiber amplifiers are cascaded in series, noise is accumulated, preventing an optical receiver from normally restoring a light signal.
SUMMARY OF THE INVENTION
To solve the above problems, it is an objective of the present invention to provide an optical fiber amplifier having a low noise property which can reduce noise even when the intensity of a light signal is low or high.
Accordingly, to achieve the above objective, there is provided an optical fiber amplifier having a low noise figure, comprising: a pump laser diode (LD) for applying a pump light to amplify an incident signal light; a first wavelength selective coupler (WSC) for coupling the incident signal light and the pump light output from the pump LD into an optical fiber; a first optical fiber medium for amplifying the incident signal light applied from the first WSC using the pump light of the pump LD; a second optical fiber medium acting as an absorption medium for reducing a high amplification factor in a predetermined wavelength range of a signal light using an absorption spectrum of an optical fiber medium; a third optical fiber medium for amplifying a signal light using a residual pump light of the first optical fiber medium; a second WSC for separating the light output from the first optical fiber medium into a signal light and a pump light to prevent the residual pump light of the first optical fiber medium from being applied to the second optical fiber medium, and applying the signal light to the second optical fiber medium; and a third WSC for coupling the pump light divided by the second WSC and the signal light whose amplification factor is reduced by the second optical fiber medium, into an optical fiber, and applying the result to the third optical fiber medium.
The first, second and third optical fiber media are erbium doped fibers (EDF). The optical fiber amplifier having a low noise figure further comprises: a first isolator for preventing amplified spontaneous emission (ASE), caused when a pump light is incident from the first optical fiber medium, from proceeding in a direction where a light signal is incident; and a second isolator for preventing a light signal amplified by the third optical fiber medium from being reflected and reentering the third optical fiber medium.
BRIEF DESCRIPTION OF THE DRAWINGS
The above objective and advantage of the present invention will become more apparent by describing in detail a preferred embodiment thereof with reference to the attached drawings in which:
FIG. 1 is a block diagram illustrating the configuration of a conventional single forward erbium doped fiber amplifier (EDFA);
FIG. 2 is a graph illustrating a signal-to-gain property curve for the conventional optical fiber amplifier;
FIG. 3 is a graph illustrating a signal-to-noise property curve for the conventional optical fiber amplifier;
FIG. 4 is a block diagram illustrating the configuration of an optical fiber amplifier according to an embodiment of the present invention;
FIG. 5 illustrates an absorptionlemission spectrum of the normal EDFA; and
FIG. 6 illustrates an absorption spectrum of an erbium doped fiber (EDF) used in the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 4, an optical fiber amplifier according to an embodiment of the present invention is comprised of a first isolator 400, a pump laser diode (LD) 410, a first wavelength selective coupler (WSC) 420, a first erbium doped fiber (EDF) 430, a second WSC 440, a second EDF 450, a third WSC 460, a third EDF 470 and a second isolator 480.
The pump LD 410 applies a pump light to amplify an incident light signal.
The pump light has a 980nm wavelength band. The first WSC 420 couples the incident light signal and the pump light output from the pump LD 410 into an optical fiber.
The first EDF 430 is a fiber amplifying medium for amplifying the incident light signal applied from the first WSC 420 using the pump light of the pump LD 410. The first isolator 400 prevents amplified spontaneous emission (ASE), caused when the first EDF 430 receives the pump light, from reentering an input port through which the light signal is incident.
The second EDF 450 acts as an absorption medium for reducing a high amplification factor in a 1530nm wavelength band of the light signal using an absorption spectrum of an EDF. The third EDF 470 is a fiber amplifying medium for amplifying a light signal using a residual pump light from the first EDF 430.
The second WSC 440 separates a light output from the first EDF 430 into lights of 980nm and 1550nm. The second WSC 440 separates the output light of the first EDF 430 into a signal light and a pump light to prevent the residual pump light of the first EDF 430 from being applied to the second EDF 450, and applies the signal light to the second EDF 450. The third WSC 460 couples the pump light divided by the second WSC 450 and a light signal whose amplification factor is reduced by the second EDF 450, into an optical fiber, and applies the result to the third EDF 470. The second isolator 480 prevents a light signal amplified by the third EDF 470 from being reflected and reentering the third EDF 470.
The operation of an embodiment of the present invention will now be described on the basis of the above-described configuration. First, the incident light signal passes through the first isolator 400, and is coupled to the pump light generated by the pump LD 410 by the first WSC 420. Then, the light signal is primarily amplified by the pump light applied from the first WSC 420 to the first
EDF 430, and the amplified signal is applied to the second EDF 450 via the second WSC 440. Here, pump power is not applied to the second EDF 450 but to the third WSC 460 via the second WSC 440.
As shown in the optical spectrum applied to the second EDF 450 of FIGS. 5 and 6, absorption is large in a 1530nm wavelength band, and small in a 1550nm wavelength band, according to the absorption level depending on the wavelength of the second EDF 450. FIG. 5 shows an absorption/emission spectrum of a normal EDFA, and FIG. 6 shows an absorption spectrum of an EDF used in the present invention.
The output light of the second EDF 450 having an intensity that varies according to the absorption spectrum of the second EDF 450 is secondly amplified according to the pumping power applied from the third WSC 460 and the amplification factor of the third EDF 470. When high ASE power in a 1530nm wavelength band is reduced by the second EDF 450, an amplification factor in the 1530nm wavelength band is lowered in the third EDF 470, but an amplification factor in a 1550nm wavelength band is increased to improve gain. When ASE power level is also reduced in the second EDF 450 over the entire amplification wavelength range, ASE at the wavelength of a signal finally amplified by the third
EDF 470 is also reduced. The N.F. decreases with a reduction of PASE. As a result of measuring the input signal light from -35dBm to OdBm, N.F. is very constant, being at maximum in a range between 4.9dB and 5.6dB.
According to the present invention, noise figure is reduced even when the intensity of a light signal applied to an optical fiber amplifier is low or high, thus preventing reception sensitivity from being degraded when an optical receiver receives a light signal which is amplified and transmitted.
Claims (6)
1. An optical fiber amplifier having a low noise figure, comprising:
a pump laser diode (LD) for applying a pump light to amplify an incident signal light;
a first wavelength selective coupler (WSC) for coupling the incident signal light and the pump light output from the pump LD into an optical fiber;
a first optical fiber medium for amplifying the incident signal light applied from the first WSC using the pump light of the pump LD;
a second optical fiber medium acting as an absorption medium for reducing a high amplification factor in a predetermined wavelength range of a signal light using an absorption spectrum of an optical fiber medium;
a third optical fiber medium for amplifying a signal light using a residual pump light of the first optical fiber medium;
a second WSC for separating the light output from the first optical fiber medium into a signal light and a pump light to prevent the residual pump light of the first optical fiber medium from being applied to the second optical fiber medium, and applying the signal light to the second optical fiber medium; and
a third WSC for coupling the pump light divided by the second WSC and the signal light whose amplification factor is reduced by the second optical fiber medium, into an optical fiber, and applying the result to the third optical fiber medium.
2. The optical fiber amplifier having a low noise figure as claimed in claim 1, wherein the first, second and third optical fiber media are erbium doped fibers (EDF).
3. The optical fiber amplifier having a low noise figure as claimed in any of claims 1 and 2, further comprising:
a first isolator for preventing amplified spontaneous emission (ASE), caused when a pump light is incident from the first optical fiber medium, from proceeding in a direction where a light signal is incident; and
a second isolator for preventing a light signal amplified by the third optical fiber medium from being reflected and reentering the third optical fiber medium.
4. The optical fiber amplifier having a low noise figure as claimed in claim 3, wherein the pump light generated by the pump LD has a 980nm wavelength band.
5. The optical fiber amplifier having a low noise figure as claimed in claim 3, wherein the second EDF is an absorption medium for reducing a high amplification factor in a 1530nm wavelength band using an absorption spectrum of an optical fiber medium.
6. An optical fiber amplifier substantially as described with reference to
figures 4 to 6 of the accompanying drawings.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| KR1019970029325A KR19990005152A (en) | 1997-06-30 | 1997-06-30 | Low Noise Optical Fiber Amplifier |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB9813874D0 GB9813874D0 (en) | 1998-08-26 |
| GB2326996A true GB2326996A (en) | 1999-01-06 |
Family
ID=19512371
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9813874A Withdrawn GB2326996A (en) | 1997-06-30 | 1998-06-29 | Optical fibre amplifier with absorption medium to reduce noise |
Country Status (3)
| Country | Link |
|---|---|
| JP (1) | JPH1187821A (en) |
| KR (1) | KR19990005152A (en) |
| GB (1) | GB2326996A (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR100353418B1 (en) * | 1999-03-11 | 2002-09-18 | 삼성전자 주식회사 | Manufacturing erbium doped optical fiber formed grating therein and optical fiber amplifier using it |
Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0695050A1 (en) * | 1994-07-25 | 1996-01-31 | PIRELLI CAVI S.p.A. | Amplified telecommunication system for wavelength-division multiplexing transmissions capable of limiting variations in the output power |
-
1997
- 1997-06-30 KR KR1019970029325A patent/KR19990005152A/en not_active Application Discontinuation
-
1998
- 1998-06-29 GB GB9813874A patent/GB2326996A/en not_active Withdrawn
- 1998-06-29 JP JP10181902A patent/JPH1187821A/en active Pending
Patent Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0695050A1 (en) * | 1994-07-25 | 1996-01-31 | PIRELLI CAVI S.p.A. | Amplified telecommunication system for wavelength-division multiplexing transmissions capable of limiting variations in the output power |
Also Published As
| Publication number | Publication date |
|---|---|
| GB9813874D0 (en) | 1998-08-26 |
| KR19990005152A (en) | 1999-01-25 |
| JPH1187821A (en) | 1999-03-30 |
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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) |