Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04J—MULTIPLEX COMMUNICATION
  • H04J14/00—Optical multiplex systems
  • H04J14/06—Polarisation multiplex systems
• • 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
  • G02B6/26—Optical coupling means
  • G02B6/27—Optical coupling means with polarisation selective and adjusting means
  • G02B6/2706—Optical coupling means with polarisation selective and adjusting means as bulk elements, i.e. free space arrangements external to a light guide, e.g. polarising beam splitters
  • G02B6/2713—Optical coupling means with polarisation selective and adjusting means as bulk elements, i.e. free space arrangements external to a light guide, e.g. polarising beam splitters cascade of polarisation selective or adjusting operations
  • G02B6/272—Optical coupling means with polarisation selective and adjusting means as bulk elements, i.e. free space arrangements external to a light guide, e.g. polarising beam splitters cascade of polarisation selective or adjusting operations comprising polarisation means for beam splitting and combining
• • 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
  • G02B6/26—Optical coupling means
  • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
  • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
  • G02B6/29379—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means characterised by the function or use of the complete device
  • G02B6/29392—Controlling dispersion
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04J—MULTIPLEX COMMUNICATION
  • H04J14/00—Optical multiplex systems
  • H04J14/08—Time-division multiplex systems

Definitions

• the invention relates to an improved method for the optical transmission of a polarization multiplex signal.
• the transmission of data in polarization multiplex operation is a promising method to double the transmission capacity without having to make higher demands on the transmission path or the signal-to-noise ratio.
• PMD polarization mode dispersion
• the process is easy to implement.
• the carrier signals of both optical data signals (Polmux channels) derived from the same laser are shifted in phase by a constant 90 ° relative to one another. Both carrier signals therefore of course have exactly the same frequency and their phase difference remains constant during transmission.
• the transmitter-side phase setting can be carried out using different elements such as phase modulators and delay elements.
• phase control which ensures a constant phase difference between the carrier signals, regardless of the environmental conditions and component tolerances.
• FIG. 1 shows a basic circuit diagram of the transmission arrangement
• FIG. 2 shows a basic circuit diagram with phase control
• FIG. 3 shows an arrangement for measuring the phase difference
• FIG. 4 shows another arrangement for measuring the phase difference
• FIG. 5 shows an arrangement for measuring the phase difference by evaluating orthogonal signal components.
• Figure 1 shows a basic circuit diagram of the transmission arrangement.
• the method can be implemented by any modified arrangements.
• a light signal CW (constant wave) usually generated by a laser is fed via an input 1 to a polarization splitter 2, which splits it into two orthogonal carrier signals CW X and CW Y of the same amplitude, but which have different polarization planes by 90 ° ⁇ the arrows indicate the respective polarization).
• the first orthogonal carrier signal CW is fed via a first optical fiber 3 to a first modulator 5, where it is intensity-modulated with a first data signal DS1.
• the second orthogonal carrier signal CW Y is transmitted via a second ser 4 and a phase shifter 6 are fed to a second modulator 7 and there intensity is modulated with a second data signal DS2.
• the optical data signals OS1 and 0S2 emitted at the outputs of the modulators, which are polarized orthogonally to one another and have a phase shift of their carrier signals by 90 °, are combined in a polarization combiner 8 to form a polarization multiplex signal (Pol ux signal) PMS and on Output 9 delivered. Both the phase shift between the carrier signals and the adjustment of the polarization can also take place after the modulators.
• FIG. 2 shows such a variant, in which the carrier signal CW is first divided into two equal parts CW1 and CW2 in a power splitter 13, which are each modulated as carrier signals with one of the data signals DS1 and DS2.
• the conversion into orthogonal optical data signals OS1 and OS2 is achieved by two polarization controllers 14 and 15, which are arranged in front of the polarization combiner 8 and then of course also convert the carrier signals CW1 and CW2 into the orthogonal carrier signals CW X and CW Y.
• the phase shift between the carrier signals CW1 and CW2 is produced by a regulated phase shifter 10 (phase modulator, delay element), which is controlled by a control device 11.
• the control device 11 receives, via a measuring splitter 12, a measuring signal MS of lower power corresponding to the Polmux signal PMS and monitors the phase shift between the carriers of the orthogonal data signals OS1 and OS2.
• the time constant of the control device is chosen to be very large, so that the controlled phase shifter 10 practically has a constant value.
• the phase shifter 10 can also be connected downstream of the polarization adjuster 15.
• the phase shift of the carrier signals can thus be carried out by setting the carrier signals CW X and CW Y or CWl and CWs or the orthogonal data signals OS1 and 0S2.
• a control criterion for the carrier phases can be obtained with little effort whenever both Polmux channels transmit a signal at the same time, for example when both signals correspond to a logical one.
• FIG. 3 shows a basic circuit diagram of the control device for obtaining a control criterion.
• the measuring principle is based on the fact that the "state of polarization" depends on the phase between the two polarized signals OS1 and OS2, and thus the phase difference can in turn be determined by measuring the polarization state. Only the measurement of the circular polarization component is required. To measure them, the measurement signal MS, which like the Polmux signal has a certain polarization, is split into two sub-signals, one of which is passed through a ( ⁇ / 4 plate and a 45 ° polarizer (polarization filter).
• FIG. 4 shows a further possibility for determining the phase difference by using a so-called DGD element (differential group delay element), for example a polarization-maintaining fiber or a birefringent crystal, which reverses the 90 "phase shift of the carrier signals, so that their superimposition when Output signal RTS results in a maximum (or with opposite phase shift a minimum) of power.
• DGD element differential group delay element
• the polarization planes of the orthogonal signals OS1 and OS2 should be 45 ° with respect to the main axes of the DGD element.
• FIG. 5 shows a further arrangement with which it is possible to regulate the phase.
• the prerequisite is again that the Polmux signal PMS or the corresponding measurement signal MS has a certain polarization, as is the case with the transmitter anyway.
• the Polmux signal or measurement signal here has two (at least almost) orthogonal signals OS1 and OS2, which are polarized at + 45 ° and -45 ° with respect to a polarization plane of the polarization splitter 24.
• the measurement signal MS which represents both orthogonal signals OS1 and 0S2, is broken down by the polarization splitter 24 into two polarized signal components OS x and 0S Y , which thus each contain signal components of both orthogonal signals OS1 and OS2.
• the signal components MS X and MS Y are converted separately into electrical signal components E x and E ⁇ in photodiodes 18 and 19. Only when there is a certain phase between the orthogonal signals OS1 and OS2 will both signal components MS X and MS Y be the same size.
• a corresponding criterion EA - EB can be used for regulation.
• the sensitivity of the control can be increased by special signal processing in the control device 25, for example by multiplying the signal components.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Chemical & Material Sciences (AREA)
• Dispersion Chemistry (AREA)
• Optical Communication System (AREA)

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• 2004
  • 2004-02-05 DE DE102004005718A patent/DE102004005718A1/de not_active Ceased
• 2005
  • 2005-01-27 US US10/588,023 patent/US7715730B2/en not_active Expired - Fee Related
  • 2005-01-27 CN CN2005800041301A patent/CN1918837B/zh not_active Expired - Fee Related
  • 2005-01-27 EP EP05707871A patent/EP1712025A1/de not_active Withdrawn
  • 2005-01-27 WO PCT/EP2005/050353 patent/WO2005076509A1/de not_active Application Discontinuation

Patent Citations (2)

Non-Patent Citations (2)

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