Classifications

• • 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
  • H04B10/293—Signal power control
  • H04B10/294—Signal power control in a multiwavelength system, e.g. gain equalisation
  • H04B10/296—Transient power control, e.g. due to channel add/drop or rapid fluctuations in the input power
• • 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
  • 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
  • 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
  • H04B10/293—Signal power control
  • H04B10/294—Signal power control in a multiwavelength system, e.g. gain equalisation
• • 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

Definitions

• the invention relates to a fiber amplifier for wavelength division multiplexing.
• Wavelength division multiplexing offers the possibility of increasing the transmission capacity of optical transmission systems.
• fiber amplifiers are provided, which usually amplify all signals transmitted in different channels together.
• the amplifiers In order to avoid differences in quality in the transmitted signals as much as possible, the amplifiers must amplify in all channels as equally as possible: in the wavelength range used, therefore, have a flat “gain spectrum” (a uniform amplification).
• the total power at the output of an amplifier is usually kept constant with the aid of a control loop. If, however, the sections of the route between the amplifiers have different attenuations, then the amplifiers are operated with different input powers and therefore with different amplifications in order to keep the output power constant. Without additional measures, however, the required flat gain spectrum then "tilts", i.e. that different amplifications occur for different wavelengths, so that the flat gain spectrum (gain) plotted over the wavelength rotates
• Tilts This is the case with fiber amplifiers that are doped with ions from the rare earth group.
• the problem of this gain spectrum tilting is kept within limits by restricting the permissible signal power range at the inputs of the optical fiber amplifiers. If the signal levels at the inputs of the individual amplifiers deviate only slightly from one another, the resulting level deviations between the individual channels can usually still be compensated for by system reserves at the end of a transmission path.
• the object of the invention is to provide a fiber amplifier whose gain spectrum practically does not change in the wavelength range used with different input powers.
• the use of two amplifier stages connected in a chain is particularly advantageous, an attenuator being inserted between the amplifier stages.
• an attenuator By connecting the amplifier stages in series, a higher gain can be achieved and a large input power range can be processed.
• a constant input level is fed to the second amplifier and through the attenuator, so that the output level can be controlled both for a constant gain and for a constant output signal.
• the gain With the controllable attenuator, the gain can be kept constant at different input powers, so that the output spectrum does not tilt (gain tilt).
• the gain (gain) of both amplifier stages is designed so that compensate for their drop in profits as much as possible. A desired tilt can also be set.
• the use of at least two separate amplifier stages enables very favorable noise characteristics, since the first optical amplifier can be optimized with regard to noise.
• the arrangement of the attenuator between the amplifiers has the advantage that only the lower output power of the first optical amplifier is attenuated and less power losses occur than when the attenuator is attached to the output of the second optical amplifier. This arrangement is also favorable with regard to the noise behavior.
• more than two amplifier stages can also be provided. Additional controllable attenuators can be inserted between these additional amplifier stages.
• Figure 1 shows a preferred embodiment of the invention
• Figure 2 shows the basic circuit diagram of a regulated amplifier stage.
• FIG. 1 shows the series connection of a first optical amplifier stage OV1, a controllable attenuator DG, an optical filter OF and a second optical amplifier stage 0V2 shown.
• An optical signal OS fed to the input 1 of the series circuit is amplified by a constant factor and then reduced to a constant level by the controllable attenuator DG.
• the second optical amplifier stage amplifies this signal (mostly) to a desired constant output level, which is present at output 2.
• both the output level and the gain can be regulated to a constant value. Due to the constant gain (amplification), there is no tilting (distortion) of the gain spectrum (signal spectrum). Any remaining deviations of the resulting output spectrum of the entire amplifier from the ideal flat profile can be compensated for with the aid of a fixed filter inserted between the amplifiers.
• HP8158B from HEWLETT PACKARD are well-known industrial products.
• a controllable optical amplifier stage OV is shown in FIG.
• the amplifier part consists of a pump coupler PK, via which pump radiation from a pump laser PL is coupled, and a doped fiber FA.
• the input power at input E is measured via a first coupler KOI and an optical receiver OE1; via a second one arranged at the output A of the optical amplifier
• Coupler K02 and a second optical receiver 0E2 the output power is measured and, after the attenuation of the corresponding electrical signal in an attenuator KD, compared with the input power in a laser control LS.
• the pump laser PL is readjusted accordingly so that the gain (gain) is constant. It can both the total output power as well - if appropriate selective evaluation - the power of a particular signal can be used for control.
• the control can be modified in the second optical amplifier of the circuit shown in FIG. Both a comparison between the input power and a constant output value and the output power with a constant reference value can be compared, i.e. the output variable is kept constant.
• regulation of the second amplifier stage can be dispensed with, since its input signal is constant and the amplification can be set to be sufficiently constant via the pump laser.
• the entire fiber amplifier is optimized with regard to its noise behavior, in particular by optimizing its first amplifier stage with regard to its noise behavior as part of the required amplification.
• the noise behavior deteriorates somewhat again due to the attenuator, this effect is negligible due to the gain of the first amplifier stage, which clearly exceeds the attenuation.
• a further amplifier stage can also be connected upstream or downstream of the fiber amplifier shown in FIG. 1, further controllable attenuators and optical filters being inserted if necessary.

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• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Plasma & Fusion (AREA)
• Optics & Photonics (AREA)
• Lasers (AREA)
• Optical Communication System (AREA)

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Publications (1)

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• 1997
  • 1997-11-27 WO PCT/DE1997/002782 patent/WO1998028826A1/de not_active Application Discontinuation
  • 1997-11-27 EP EP97949971A patent/EP0898798A1/de not_active Withdrawn
  • 1997-11-27 CN CN 97193928 patent/CN1216641A/zh active Pending
  • 1997-11-27 RU RU98117454/09A patent/RU98117454A/ru not_active Application Discontinuation
  • 1997-11-27 AU AU53092/98A patent/AU5309298A/en not_active Abandoned
  • 1997-11-27 JP JP10528209A patent/JP2000505954A/ja active Pending

Non-Patent Citations (1)

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