Method and device for measuring polarization mode dispersion

Abstract

Apparatus for measuring polarization mode dispersion (PMD) of a device, e.g. a waveguide, comprises a broadband light source ( 10,12 ) for passing polarized broadband light through the device ( 14 ), an interferometer ( 20 ) for dividing and recombining light that has passed through the device to form interferograms, a polarization separator ( 30 ) for receiving the light from the interferometer and separating such received light along first and second orthogonal Feb. 25, 2003 Feb. 25, 2003 polarization states, detectors ( 32 x ,32 y) for converting the first and second orthogonal polarization states, respectively, into corresponding first and second electrical signals (Px(tau),Py(tau)), and a processor ( 36 ) for computing the modulus of the difference and such, respectively, of the first and second electrical signals to produce a cross-correlation envelope (EC(tau)) and an auto-correlation envelope (Ec(tau)), and determining the polarization mode dispersion according to the expression PMD=where and tau is the delay difference between the paths of the interferometer. PMD = 3 2 ⁢ ( sigma 2 - sigma 0 2 ) ⁢ ⁢ sigma 2 = ∫ tau 2 ⁢ E C 2 ⁡ ( tau ) ⁢ ⅆ tau ∫ E C 2 ⁡ ( tau ) ⁢ ⅆ tau ⁢ ⁢ and ⁢ ⁢ sigma 0 2 = ∫ tau 2 ⁢ E A 2 ⁡ ( tau ) ⁢ ⅆ tau ∫ E A 2 ⁡ ( tau ) ⁢ ⅆ tau ( I )

Description

technical field [0001] The present invention relates to methods and apparatus for measuring the polarization mode dispersion (PMD) of optical devices, in particular waveguides used in optical communication systems. Background technique [0002] It is known that PMD can be measured by injecting broadband linearly polarized light into a waveguide, passing the light exiting the waveguide through a linear polarizer, and sending it to a scanning interferometer, where the light exiting the two arms of the interferometer is combined to produce An interferogram, converting the intensity I of said composite light into a corresponding electrical signal, and processing this electrical signal to obtain the PMD from the curve I(τ), which is the intensity I of the light relative to the interferometer The curve of the optical path delay difference τ (hereinafter referred to as delay τ) between the two arms. [0003] As described in US Pat. No. 5,712,704 (Martin et al.), the curve I(τ) exh...

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Problems solved by technology

[0005] However, both of the above methods are not completely satisfactory, because they are based on the removal of the "parasitic" central peaks because they hinder the measurement of PMD, so that the measurement accuracy can be significantly improved by simply removing the central peaks

This is only partially true, in practice removing the central peak means discarding useful information, with the result that very small PMDs approaching 0 cannot be accurately measured

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