WO2006094407A1 - Emulateur de dispersion de mode de polarisation - Google Patents

Emulateur de dispersion de mode de polarisation Download PDF

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Publication number
WO2006094407A1
WO2006094407A1 PCT/CA2006/000366 CA2006000366W WO2006094407A1 WO 2006094407 A1 WO2006094407 A1 WO 2006094407A1 CA 2006000366 W CA2006000366 W CA 2006000366W WO 2006094407 A1 WO2006094407 A1 WO 2006094407A1
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Prior art keywords
sections
pmd
smf
mode dispersion
polarization mode
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PCT/CA2006/000366
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English (en)
Inventor
Yannick Keith Lize
Nicolas Godbout
Suzanne Lacroix
Leigh Palmer
Raman Kashyap
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Corporation De L'ecole Polytechnique De Montrea L
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Publication of WO2006094407A1 publication Critical patent/WO2006094407A1/fr

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    • 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
    • G02B6/2753—Optical coupling means with polarisation selective and adjusting means characterised by their function or use, i.e. of the complete device
    • G02B6/278—Controlling polarisation mode dispersion [PMD], e.g. PMD compensation or emulation

Definitions

  • the present invention generally relates to polarization mode dispersion emulators. More specifically, the present invention is concerned with polarization mode dispersion emulators using a single modified Lefevre controller.
  • PMD in a fiber arises from geometric or stress anisotrophy in the fiber core.
  • the breakdown of circular symmetry induces modal birefringence in the fiber and thus two distinct polarization modes propagate at different speeds. If the birefringence axes of the fiber are fixed, only a simple W
  • DTD differential group delay
  • the net PMD is obtained by taking the vector sum of each of the section contributions rotated into the same reference frame. Selecting the reference frame of the last section the net output PMD vector is given by:
  • ⁇ N is the physical orientation of the waveplate
  • RN- I is the rotation matrix
  • ⁇ denotes the angular frequency
  • emulator designs demonstrated in the literature are typically based on concatenating a number of highly birefringent elements.
  • PC polarization controllers
  • rotatable connectors or by thermally tuning the birefringence of the elements
  • independent mode coupling is implemented using a number of sections with separate polarization rotating devices. Since higher orders of PMD require an increasing number of emulator sections for their statistics to be accurately reproduced, the design has poor scalability. In practice, the number of sections required is typically limited to 30. Hence 30 polarization controllers are required.
  • variable DGD elements Any desired first order statistic can be obtained by deterministically controlling the DGD of the elements.
  • This technique can emulate the first-order PMD with exact Maxwellian distribution by using only one DGD element but more are necessary for the generation of higher order PMD.
  • the principal advantage is that a wide range of mean DGD can be obtained but the method requires more complex control.
  • Variable DGD elements are more expensive than polarization controllers and have larger insertion losses and do not offer any advantage in the number of sections needed for low background autocorrelation.
  • a PMD emulator should emulate the proper statistical behavior of a transmission link for all orders of PMD and have a frequency autocorrelation function that tends to zero outside a limited bandwidth with the least number of elements possible. It should preferably be simply controlled, have a low insertion loss, low polarization-dependent loss and have flexible design parameters for low-cost manufacturing.
  • An object of the present invention is therefore to provide a polarization mode dispersion emulator which replaces the multiple coupling stages of a conventional emulator with a single modified Lefevre polarization controller (PC).
  • PC Lefevre polarization controller
  • Another object of the present invention is to provide a polarization mode dispersion emulator which is robust, compact, low-cost, having low polarization-dependent loss, low insertion loss and being flexible in design parameters.
  • Another object of the present invention is to provide a polarization mode dispersion emulator which is scalable.
  • a polarization mode dispersion (PMD) emulator comprising a single mode fiber (SMF) signal input section, a SMF signal output section, first intermediate SMF sections between the input and the output sections, and second intermediate SMF sections between the input and the output sections.
  • the first intermediate SMF sections are spooled about respective movable spooling members.
  • each of the second intermediate SMF sections is spliced with a respective polarization maintaining fiber (PMF) section, each of the PMF sections having a length defined by a fiber length distribution.
  • the SMF signal input section, the first and second intermediate SMF sections, the PMF sections and the SMF signal output section define a series circuit with the first and second intermediate SMF sections alternating relative to one another.
  • Figure 1 is a schematic diagram of a PMD emulator using a single PC according to an embodiment of the present invention
  • Figures 2a, 2b and 2c illustrate examples of PC rotation distributions according to the Poincare sphere
  • Figure 3 illustrates the probability density function vs DGD from simulating the embodiment according to the present invention as illustrated in Figure 1.
  • Figure 4 is a graph showing the Normalized Deviation Factor vs the number of sections for the first order statistics
  • Figure 7 is a graph illustrating the simulated auto-correlation function of an emulator using a single modified controller
  • Figure 8 is a graph illustrates the background auto-correlation vs the number of sections.
  • FIG. 1 illustrates a PMD emulator 10 in accordance with an embodiment of the present invention.
  • the PMD emulator 10 can be described via a vector ⁇ ( ⁇ ) in the Stokes space, where ⁇ is the angular optical frequency [G. Foschini and C. Poole, "Statistical theory of polarization dispersion in single mode fibers," J. Lightwave Technol., vol. 9, no. 11, pp. 1439-1456, 1991].
  • the PMD vector is derived from the frequency dependence of the Jones matrix [B. L. Heffner "Deterministic, analytically complete measurement of polarization-dependent transmission through optical devices", Photon. Tech. Lett., 4(5), 451-454 (1992)] expressed as:
  • R is the rotation matrix
  • ⁇ n represents the axis of alignment for the n th section
  • PC is the transfer matrix for the PC of the n th section
  • ⁇ n [ ⁇ - ⁇ n , ⁇ 2 ⁇ , ⁇ 3n ] are the angles of each of the three paddles of the PC
  • ⁇ n [ ⁇ i n , ⁇ 2n, ⁇ 3 ⁇ ] are the differential phase delays of each paddle.
  • B( ⁇ n , ⁇ ) is the frequency dependent transfer matrix for the element of the n th section with fixed DGD ⁇ n .
  • the DGD (Differential Group Delay) for the PMD emulator can be found by calculating the eigenvalues of the matrix ⁇ ⁇ T( ⁇ )T 1 ( ⁇ ).
  • the PMD emulator 10 is part of a new class of multi-section PMD emulators employing degenerate polarization scrambling (DPS) for which the matrices describing the polarization rotations are correlated. Typically this would be due to PC component reuse.
  • DPS degenerate polarization scrambling
  • SSMF standard single mode fiber
  • PMF polarization maintaining fiber
  • the rotation matrix associated with the j th polarization scrambling stage is given by the product of the M ⁇ ller matrices describing the retardations due to the three PC paddles:
  • the fixed waveplate retardations can be arbitrarily chosen by winding the SMF for each PC stage a different number of turns around the paddles, thus allowing degeneracy to be at least partially broken.
  • first and second intermediate SMF sections 17 and 19 respectively alternate relative to each other.
  • a plurality of such alternating first and second intermediate SMF sections 17 and 19 can be defined and are referred to as the number of sections.
  • Such number of turns around the paddles 16 is chosen arbitrarily according tho the needs of the skilled artisan in the art.
  • several parameters can be determined, such as the number of sections N, the differential group delay (DGD) ⁇ n , the length of each PMF section 20, the splicing angle ( ⁇ n ) between SMF and PMF sections, and the phase delays ( ⁇ n ) of the paddles 16 in order to produce a PMD emulator.
  • the SMF 12 is a standard single mode fiber, well known in the art. Consequently, SMFs will not be further discussed in the present specification.
  • the paddles 16 are generally motorized and rotated continuously using generic electrical motors (not shown). Each motor has a constant speed but a slightly different constant voltage is applied to each one of the motors. Thus, by randomly moving/rotating the paddles laterally with respect to the direction of input signals, the mode coupling between each one of the paddles of the PC is randomly varied, which allows for generating different PMD states. It has been shown that three such paddles 16 can generate any desired polarization states, even though it is not necessary to have three paddles. Simulations with two paddles showed poor performance of the emulator. Of course, four or more such paddles 16 can be used. However, an increased number of paddles greatly increases the complexity of the PMD emulator 10. The tradeoff between gain in performance and complexity depends on the needs of the intended application of the PMD emulator 10. Furthermore, the design of the paddles 16 allows for multiple independent fibers to be spooled as illustrated in Figure 1.
  • the diameter of the paddles 16 are such that a relative phase delay of ⁇ r/6 is induced per turn at a wavelength of 1550 nm when using standard single mode fiber.
  • Figures 2a, 2b and 2c illustrate the spanning of the Poincare sphere for different PC configurations where the three coupling angles between paddles are randomly varied.
  • the polarization rotation may no longer be uniformly distributed as shown for the non-uniform longitudinal spanning configurations. Correlation between stages is therefore reduced by ensuring that only PCs applying a rotation that uniformly spans the longitudinal angles on the Poincare sphere are used.
  • PMF 20 is provided for splicing to each respective section of the SMF 12.
  • Each section of PMF 20 has a different length which is determined by a PMF length distribution function.
  • Such length distribution function includes uniform distribution (equal length for each section), exponential distribution, Gaussian distribution and Maxwellian distribution.
  • the number of sections is arbitrary and will depend on the needs of the intended application. The larger is the number of sections, the higher is the order of the PMD statistical distribution that can be established.
  • An example showing the parameters used in a PMD emulator 10 is given in Table 1.
  • the PMD emulator 10 design limits the number of variables for accessing different PMD states to the three coupling angles between the PC paddles (since three paddles 16 are used in an embodiment of the present invention).
  • Another embodiment of the present invention is concerned with the deterministic case when the rotating paddles are given specific values. By doing so, a table of values can be generated and then used to map the characteristics of the PMD.
  • a first scenario for experimental setup for Monte Carlo simulations consists of:
  • a second example uses the same information as given in the first scenario with the exception that the PMF length is distributed with a Gaussian distribution this time. Furthermore, further simulations have been performed with the number of sections N set to 15, 30 and 50.
  • a commonly used parameter to analyze the statistics of a PMD emulator is the deviation factor defined as ⁇ /
  • PDFemui(Xi) and PDFtheory(Xi) are probability density functions for the emulator and the theoretical prediction for a long fiber link for the PMD order considered.
  • this definition has the disadvantage of overestimating the importance of theoretical PDF matching in the peak of the distribution at the expense of the tail where system outages are most likely to occur.
  • a normalized deviation factor which puts more emphasis in the tail of the distribution.
  • the graph of Figure 4 compares the normalized deviation factor of first order PMD as a function of the number of sections for the single PC emulator versus a standard independent scrambling stages emulator. It indicates that independent polarization scrambling leads to better results for the same number of sections.
  • the main advantage of the single PC design is that it is scalable so that a 50 section single PC emulator is much easier to fabricate than a 15 sections independently controlled emulator and provides much better theoretical match.
  • the graph of Figure 5 compares the second order statistcs of the two types of emulator from which the same conclusion can be drawn.
  • the auto-correlation functions tend to zero with just a few sections in a standard independently scrambled PMD emulator design as shown in the graph of Figure 6. In the single PC emulator design, a similar behavior is observed as shown in the graph of Figure 7. Plotting the simulated background auto-correlation vs the number of sections in the graph of Figure 8 indicates that both design provide similar performance for broadband PMD emulation even though a single PC design is a much simpler device.
  • a three element variable DGD PMD emulator which provides very good first and second order statistics, has around 50% background autocorrelation which makes them unsuitable in the testing of broadband PMD mitigation strategies.

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  • Physics & Mathematics (AREA)
  • Chemical & Material Sciences (AREA)
  • Dispersion Chemistry (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Optical Communication System (AREA)

Abstract

L'invention concerne un émulateur de dispersion de mode de polarisation (PMD) qui comprend une partie entrée de signal de fibre monomode (SMF), une partie sortie de signal SMF, des premières parties intermédiaires SMF se situant entre les parties d'entrée et de sortie, et des deuxièmes parties intermédiaires SMF se situant entre les parties d'entrée et de sortie. Les premières parties intermédiaires SMF sont bobinées autour d'éléments de bobinage mobiles respectifs. De plus, chacune des deuxièmes parties intermédiaires SMF est épissurée avec une partie fibre de maintien de polarisation (PMF) respective, chacune des parties PMF présentant une longueur définie par une répartition de longueur de fibre. La partie entrée de signal SMF, les premières et deuxièmes parties intermédiaires SMF, les parties PMF et la partie sortie de signal SMF définissent un circuit en série avec, en alternance, les premières et deuxièmes parties intermédiaires SMF.
PCT/CA2006/000366 2005-03-10 2006-03-10 Emulateur de dispersion de mode de polarisation WO2006094407A1 (fr)

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US60/659,883 2005-03-10

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2007024542A1 (fr) * 2005-08-24 2007-03-01 Massachusetts Institute Of Technology Embrouilleurs de polarisation combinatoire destines a plusieurs emulateurs pmd de segment

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
DOS SANTOS ET AL.: "PDL effects in PMD emulators made out with HiBi fibers: building PMD/PDL emulators", PHOTONIC TECHNOLOGY LETTERS, IEEE, vol. 16, no. 2, 28 February 2004 (2004-02-28), pages 452 - 454 *
PALMER ET AL.: "Design and optimization of polarization mode dispersion emulators for low background autocorrelation", TECHNICAL DIGEST - OFC CONFERENCE, 2004, vol. 4, 6 March 2005 (2005-03-06), pages OTHT3 (3 PGS. TOTAL) *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2007024542A1 (fr) * 2005-08-24 2007-03-01 Massachusetts Institute Of Technology Embrouilleurs de polarisation combinatoire destines a plusieurs emulateurs pmd de segment
US7289689B2 (en) 2005-08-24 2007-10-30 Massachusetts Institute Of Technology Combinatorial polarization scramblers for many segment PMD emulator

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