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
  • H04B10/25—Arrangements specific to fibre transmission
  • H04B10/2589—Bidirectional transmission
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04J—MULTIPLEX COMMUNICATION
  • H04J14/00—Optical multiplex systems
  • H04J14/02—Wavelength-division multiplex systems

Definitions

• the present invention relates to a procedure and an arrangement for two-way transmission over a common fiber, more exactly an architecture to, in a common transmission fiber, create a division of traffic channels in two-way transmission with common amplification.
• the invention can be used to increase the capacity of fiber optical links and also to effect protection switching of ring networks.
• optical amplifiers operate in one direction, whereas the traffic by switches is divided into two groups, which are routed in different directions.
• WDM Widelength Division Multiplex
• FWM Full Wave Mixing
• This problem will increase in a progressive way as separation in frequencies between the channels is growing smaller and smaller.
• DWDM dense WDM
• This problem can be reduced in known way, either by specific fiber with adapted dispersion, or by controlled dispersion, when specific compensators are connected in a network consisting of ordinary fiber.
• Another problem is to protect the traffic in optical networks against breakdowns in the traffic.
• Regular protection architectures which, for instance, are put into practice with SDH (Synchronized Digital Hierarchy) in principle imply a doubling of the whole transmission network, and by that the cost of the protection will be very high.
• SDH Synchronized Digital Hierarchy
• amplifiers of reversed direction are used along the line, which also demands a doubling of the number of amplifiers.
• the present invention solves i.a. above mentioned problems by the two-way traffic that is coming in in opposite directions being routed to the optical amplifiers so that the whole traffic is amplified in common.
• the two-way traffic also can be utilized for protection of traffic in optical ring networks by frequency shifted channels carrying a copy of the traffic in the same fiber as the original but, in opposite direction compared with this.
• the invention provides a procedure for two-way communication over a common optical fiber, at which traffic is routed through a connection with channels with a plurality of optical amplifiers in between.
• a first channel group that is coming in in one direction at one side of each amplifier is routed to the input of the amplifier, and a second channel group that is coming in in opposite direction at the other side of each amplifier, also to the input of the amplifier.
• the traffic from the output of the amplifier is divided so that the first channel group is routed further at the other side of the amplifier in one direction of the connection, and the second channel group is routed further along the connection in opposite direction.
• the ordinary traffic in each node can be frequency shifted so that the ordinary traffic constitutes the first channel group, whereas the frequency shifted traffic constitutes the second channel group.
• the invention also relates to an arrangement to execute the procedure. The procedure and arrangement are defined in patent claim 1, respective 5, whereas preferred embodiments are given in the subclaims.
• FIG. 1 is a schematic illustration of the present invention
• FIG. 2 shows an alternative embodiment of the invention
• Figure 3 schematically shows a ring network that can utilize the invention.
• the invention provides a procedure and an arrangement to, in a common transmission fiber, create a division of channels in two-way transmission with common amplification.
• the invention can be used in an architecture for protection switching of ring networks, where cost reasons speak against a protection built on ordinary architecture.
• disturbances from optical unlinearity of fibers in amplified links and fiber optical networks are avoided, without the number of fiber amplifiers having to be increased.
• the disturbances are not reduced, but the two- way traffic can be utilized for protection switching in ring networks.
• the main component to realize two-way communication with common amplification is a number of wavelength selective switches.
• MEMS Integrated Micro Electro- Mechanical Systems
• polarizers are suggested.
• FIG. 1 is shown schematically an arrangement according to the invention. Two amplifiers modified according to the invention are shown interconnected with a fiber link connection. The connection 1 consists of an optical fiber. Along the fiber there are amplifiers 2 located to compensate for attenuation in the fiber.
• the amplifiers 2 can be ordinary fiber amplifiers, for instance EDFA (Erbium-Doped Fiber Amplifier) with a usable spectrum from about 1530 - 1565 nm. To make it possible for the amplifier 2 to amplify the signals that are coming from opposite directions, a division is made so that both the signals are routed to the input of the amplifier. This is effected by switches 3, for instance broadband WDM- switches .
• EDFA Erbium-Doped Fiber Amplifier
• a channel group 5, marked with light arrows is coming m from the right, and a channel group 6 marked with dark arrows from the left.
• the channel groups cover together the wave length spectrum of the amplifier.
• the switches block one of the channels groups, but allow the other to pass through, so that both the groups 5,6 are routed to the input of the amplifier 2, and are let out in respective opposite direction at the other side of the amplifier .
• Each amplifier 2 amplifies all wavelengths in one and the same direction.
• Frequency spectrum is divided into two groups of wavelength channels at the output of the amplifier 2.
• the groups now can be selected in different ways, depending on wanted system qualities.
• the channel groups are interleaved, i.e. are put together with a certain, small spectral shift. This means that channels of meeting traffic are displaced in wavelength in relation to each other. A suitably adjusted spectral shift minimizes disturbances due to Raleigh and Brilloum dispersion from meeting channels m the transmission fiber.
• Each group is given the same, dense channel distance as the amplifier 2, but are spectrally divided mto two intervals, for instance 1530-1545, respective 1546-1565 nm if the C-band of EDFA is utilized.
• Single channel distance can be 0,8 nm according to ITU- specification .
• the distribution according to (4.1) has an advantage from a transmission point of view: For a given number of channels per direction, the comparatively sparse allocation between wavelength channels running in the same direction results in a potentially low crosstalk because chiefly FWM is reduced, alternatively (4.1) allows more channels than (4.2) .
• the division (4.2) allows that simpler filters with lower selectivity can be used at both the amplifiers 2 and at the add/drop-points.
• the invention in the variant (4.1) - and with certain limitation (4.2) - provides possibility to, without increasing the number of amplifiers, make possible protection switching of traffic between all nodes in a ring network consisting of one single fiber.
• the functionality then will have the addition that
• An interleaved division can cause problems with the wavelength selectivity, i.a. when a large number of filters have to be passed through in the ring network.
• This problem is avoided because all wavelengths (with right polarization) can pass through the polarizers 4.
• a polarizer is, in addition, of a simpler construction than a multichannel filter. Otherwise the principle is similar.
• the signal "in wrong direction” that reaches the output of an amplifier 2 does not imply any problem since the supposed type of amplifier normally includes a built-in insulator. It is also to be remembered that the signal power in the amplifiers are considerably smaller than the power at the output of the amplifiers.
• a polarization retaining fiber in the links between the amplifiers is not needed, only that the polarization of respective signals are retained in the amplifier 2.
• the attenuation in the optical track originates from four switches (4 x 3dB) and from two polarizers (3 + OdB ideally) . This totally results in about 15 dB, which is compensated by the amplifier 2, but which results in increased ASE-noise, Amplified Spontaneous Emission, at higher amplification. Further contribution of noise can occur when the detector window has to be increased.
• the principles above apply, irrespective of whether the wavelengths are the same in both directions of the transmission network or not.
• Figure 3 shows the intended application of the invention as protection of the traffic in an optically amplified ring at cut off of cable at digging, weighing anchor etc.
• Figure 3 shows how the protection is applied in a network with ten add-/drop-nodes 9 (smaller arrows) and transmission links in between with a number of amplifiers (not shown) each.
• the outer track 8 is the route for regular traffic
• the inner track 7 is the opposite route for protected traffic. Both tracks are running in the same fiber.
• the protected traffic counter-clockwise consists of a slightly frequency shifted reflection (larger arrows) of all traffic clockwise in the node closest to the fiber break 10.
• the protected traffic (the copy) can be routed without deviations to the same point that normally should be passed through by the ordinary traffic (the original) .
• the traffic only has taken a detour round the place of the break of traffic.
• the principle of the invention can be applied at upgrading of existing links and networks, in order to increase the traffic capacity (number of channels) or increased network functionality (the protection) .
• the application of the invention does not create conflict with valid ITU-standards (International Telecommunications Union) because the signal lasers are allowed to have standard frequencies.
• the filters of the detectors must be sufficiently broadband to accept both ordinary and reflected (protected) traffic.
• the protection of rings can be realized in a new way:
• the protected traffic shares both a common fiber and all line amplifiers with the normal traffic .
• Upgrading of an existing optically amplified fiber network can be made without installing new fiber, and in certain cases without changing the amplifiers.
• the physical change consists of a number of components that are connected to the input and output of the amplifier.

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Citations (6)

• 1999
  • 1999-10-18 SE SE9903734A patent/SE521823C2/sv not_active IP Right Cessation
• 2000
  • 2000-10-18 WO PCT/SE2000/002015 patent/WO2001029996A1/en active Application Filing

Patent Citations (6)

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