PatentDe  


Dokumentenidentifikation EP1191320 19.04.2007
EP-Veröffentlichungsnummer 0001191320
Titel Messung der polarisationsabhängigen Eigenschaft optischer Einheiten
Anmelder Agilent Technologies, Inc. (n.d.Ges.d.Staates Delaware), Palo Alto, Calif., US
Erfinder Stolte, Ralf, 21147 Hamburg, DE
Vertreter Barth, D., Dipl.-Ing., Pat.-Ass., 71083 Herrenberg
DE-Aktenzeichen 60127060
Vertragsstaaten DE, FR, GB
Sprache des Dokument EN
EP-Anmeldetag 07.06.2001
EP-Aktenzeichen 011138864
EP-Offenlegungsdatum 27.03.2002
EP date of grant 07.03.2007
Veröffentlichungstag im Patentblatt 19.04.2007
IPC-Hauptklasse G01M 11/00(2006.01)A, F, I, 20051017, B, H, EP

Beschreibung[en]
BACKGROUND OF THE INVENTION

The present invention relates to testing of optical components in particular for communication systems.

Measurement of polarization dependent parameters like polarization dependent loss (PDL) and polarization dependent group delay PDGD (covering Differential Group Delay DGD and Polarization Mode Dispersion PMD) is of increased importance for advanced communication systems and generally described in 'Fiber Optic Test and Measurement' by Dennis Derickson, ISBN 0-13-534330-5, 1998, pages 354ff. Especially long-haul high-speed systems require that polarization properties of its components fulfill certain requirements. In general, component manufacturers address this by 100% testing of components for critical parameters. PDL nowadays in many cases is already measured 100%, PDGD may also develop to be a 100% test in manufacturing.

Today's solutions for measuring polarization dependent loss parameters are the scrambling method (applying a random variation of polarization states and comparing maximum with minimum determined loss) or the Mueller method, whereby 4 defined polarization states are measured for each wavelength point and analyzed together. The latter requires multiple measurement sweeps at predefined polarization states. These methods are either slow, if testing at multiple wavelengths is required (PDL measurement using the scrambling method), or require multiple measurement sweeps at predefined polarization states (Mueller method). Multiple sweeps are disadvantageous because measurement time is increased and require very high stability of the measurement setup because no change of polarization properties of the whole setup (between laser and DUT) is allowed between the sweeps.

US-B-6,229,606 discloses measuring of PMD of a dispersion compensation grating. An optical source generates sequential optical beams with different wavelengths. A polarization synthesizer receives the beams and produces states of polarization for each beam. The polarized beams travel sequentially through a DUT, which produces the PMD being measured, and then enter an analyzer. The analyzer measures the intensity of the received beams with the different polarizations and generates the Stokes parameters.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an improved measurement of polarization dependent parameters. The object is solved by a system according to claim 1 and a method according to claim 5. Preferred embodiments are defined by the dependent claims.

For measuring polarization dependent parameters of an optical device under test (DUT), an optical source (preferably a tunable laser) provides an optical signal through an optical polarization translator to the DUT. The polarization translator translates the polarization of the optical signal from its input to its output in a deterministic way dependent on the wavelength of the optical signal.

The polarization translator provides the translation of the polarization dependent on the wavelength preferably using birefringent properties. Accordingly, the optical source may provide a variation of the wavelength over the time, and the polarization translator provides a 'translation' of the polarization dependent on the wavelength. The parameters wavelength and frequency shall be regarded here as equivalents (related by the general equation f = c/&lgr;).

When varying the wavelength of the optical source, the polarization translator changes the polarization of the signal launched into the DUT. Tuning the wavelength of the optical source in a way that measurement points with different polarization states are covered thus allows determining polarization dependent parameters of the DUT in that particular wavelength range.

Typical polarization dependent parameters that can be analyzed by the invention are polarization dependent loss (PDL) or polarization dependent group delay PDGD (also referred to as Differential Group Delay (DGD) or Polarization Mode Dispersion (PMD)).

The uncertainty of the polarization state of the output signal may be reduced by tapping off some fraction of the signal in an appropriate way and analyzing its polarization state at each wavelength with a polarimeter or a reduced polarization analysis device like an Analyzer.

The polarization translator may be purely passive. The optical signal preferably does not hit a Principle State of the Polarization (PSP) of the polarization translator, so that the output signal will follow a trajectory (e.g. a circle) on the Poincare Sphere in a deterministic way.

The same principle of scanning the polarization can be applied to various PMD measurement techniques: For example the Jones Matrix Eigenanalysis (JME) or a novel method which is outlined in the European Patent Application No. 125089.3 (EP 1113250). In case of PMD measurements in general only two polarization states are combined to a measurement value.

In case that several measurement points (defined by the wavelength and the polarization state of the optical signal applied to the DUT) are to be analyzed together for determining a value of a polarization dependent parameter, the wavelength range for those measurement points is preferably selected that a value of the polarization dependent parameter of the DUT can be considered as substantially constant in that wavelength range.

Preferred algorithms for analyzing together several such measurement points are interpolation of neighboring measurement points, combining 4 measurement points using the Mueller Matrix analysis, or combining 2 measurement points using e.g. the Jones Matrix analysis.

The invention has various advantages compared to today's standard methods (polarization scrambling and Mueller Matrix analysis). The polarization transformation device may be purely passive, the number of measurement points can be chosen to be much smaller compared to the scrambling method, and, most important, the complete measurement can be performed within one sweep (instead of four for the Mueller Matrix Analysis). Thus, the invention allows fast measurements and is also less sensitive against e.g. environmental or mechanical disturbances.

The invention can be partly embodied or supported by one or more suitable software programs, which can be stored on or otherwise provided by any kind of data carrier, and which might be executed in or by any suitable data processing unit.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and many of the attendant advantages of the present invention will be readily appreciated and become better understood by reference to the following detailed description when considering in connection with the accompanied drawings. Features that are substantially or functionally equal or similar will be referred to with the same reference sign(s).

  • Fig. 1 shows a measurement setup according to the invention for measuring polarization dependent parameters.
  • Fig. 2 shows a representation of polarization transformation on Poincare Sphere.
  • Figs. 3 and 4 show embodiments of the polarization translator.

DETAILED DESCRIPTION OF THE INVENTION

In Fig. 1, a tunable laser 10 as an optical source provides an optical signal through an optical polarization translator 20 to an optical device under test (DUT) 30. A power meter 40 receives and detects the optical signal after passing the DUT 30. The polarization translator 20 translates the polarization of the optical signal from its input to its output in a deterministic way dependent on the wavelength of the optical signal.

A polarization analyzer 50 might be optionally coupled to the output of the polarization translator 20 in order to determine the polarization state of the output signal of the polarization translator 20.

A controller 60 is coupled to the power meter 40 for analyzing polarization dependent parameters. Preferably, the controller 60 is further coupled to the tunable laser 10 for controlling the application and variation of the provided optical signal and to the polarization analyzer 50 for receiving information about the actual polarization state of the output signal from the polarization translator 20.

When varying the wavelength of the tunable laser 10, the polarization translator 20 changes the polarization of the optical signal launched into the DUT 30. In operation, the wavelength of the tunable laser 10 is tuned in a way that optical signals with different polarization states are provided to the DUT 30. For each measuring point (defined by the wavelength and the polarization state of optical signal applied to the DUT 30), the controller 60 receives a value of power intensity determined by the power meter 40. Analyzing the power intensity values for a plurality of different measuring points thus allows determining polarization dependent parameters of the DUT 30 such as polarization dependent loss (PDL).

In a preferred embodiment, several measurement points will be analyzed together for determining a value of a polarization dependent parameter. The wavelength range for those measurement points is selected that a value of the determined polarization dependent parameter of the DUT can be considered as substantially constant in that wavelength range.

Preferably, a set of four measurement points with different polarization states is analyzed together resulting e.g. in one PDL value for the DUT. The wavelength range of the set of measurement points is thereby preferably selected to be smaller than the wavelength resolution for that measurement. In an example wherein PDL measurements are desired with a spectral resolution of 1pm, a set of measurement points with 4 different polarizations should have a spectral distance of 0.25pm. Within such wavelength range (even going further up to say 10 pm) it can be seen as sufficiently ensured with typical DUTs of present optical networks that constant PDL properties are maintained in that range.

Fig. 2 shows a representation of polarization transformation on Poincare Sphere. The polarization state Pin of the optical signal applied to the polarization translator 20 will be transformed to polarization states Pi out (with i = 1, 2, 3, ...) at the output of the polarization translator 20. In case of a waveplate (which shows purely linear birefringence) as polarization translator 20 with an orientation O, the polarization states Pi out are all located on a circle on the Poincare Sphere dependent on the wavelength &lgr; of the optical signal.

The polarization translator 20 can be implemented in several ways depending on requirements of the particular measurement to be conducted. If a PDL measurement is to be performed with a Mueller Matrix type of implementation (see for example on pages 356ff in 'Fiber Optic Test and Measurement' by Dennis Derickson, ISBN 0-13-534330-5, 1998), a set of at least four measurements has to be made with polarization states fulfilling certain requirements: they have to be significantly different, must not be located on a great circle of the Poincare Sphere, and preferably should not be located on any circle on the Poincare Sphere. A very high order waveplate that is excited by the linearly polarized signal of the tunable laser 10 can be used. The angle between the polarization of the optical signal and the optical axis of the waveplate is defined to &phgr;1. However, in this configuration the states of polarization Pi out are located on a circle that under certain circumstances won't allow conducting the Mueller Matrix type of calculation. This problem can be avoided if at least two waveplates are concatenated with their principle state of polarization PSP not aligned. This configuration would provide second order PMD, which means that the trajectory of the polarization translation function on the Poincare sphere won't be a circle anymore.

In contrast to the Mueller Matrix based PDL measurement the PMD measurement techniques mentioned before only require measurement on 2 states of polarization. There are no requirements for these States of Polarization as long as they are sufficiently different.

In a preferred implementation, a high order waveplate as the polarization translator 20 creates a phase difference between the propagating modes by its birefringence. An angle &agr;1 represents the phase difference of the two optical signals propagating in the two Eigenmodes of the waveplate device. When entering the device the phase difference is &agr;1=0. When exiting the angle is given by: &agr; 1 = 2 &pgr; &lgr; &Dgr; n L

with &Dgr;n, &lgr;, L representing the difference of the refractive indices of the two propagating polarization modes, the optical wavelength and the length of the device, respectively. If the length L of the birefringent device 20 is kept fixed and dispersive effect are neglected (which means &Dgr;n is constant over wavelength), the wavelength increment to increase &agr;1 by a given amount, say &Dgr;&agr;1 is given by: &Dgr; &lgr; &Dgr; &agr; 1 &lgr; 2 2 &pgr; &Dgr; n L

For example, if PMD measurement values are required with a spectral resolution of 1 nm (as it may be sufficient for fused couplers as DUT 30), measurement values should be taken with an interval of 0.5nm. From Equation 2, a condition (at &lgr;=1.5µm) for the polarization transformer 20 can be derived: &Dgr; n L &Dgr; &agr; 1 &lgr; 2 2 &pgr; &Dgr; &lgr; 2.3 10 - 3 m

This requirement could be fulfilled with for example a LiNbO3 waveguide or a birefringent fiber as the polarization translator 20.

In a LiNbO3 based polarization transformer 20, a Ti diffused waveguide can be implemented perpendicular to the c-axis (optical axis) of the LiNbO3 crystal (typically selected: x- or y-cut). In this configuration, the waveguide 20 has a high birefringence of &Dgr;n≈ 0.079 with a beat length LB of the two propagating modes of: L B = 2 &pgr; &lgr; &Dgr; n 21 &mgr;m

around &lgr;=1.55 µm. Therefore the requirement mentioned in Equation 3 can be fulfilled with a LiNbO3 waveguide 20 of a length of about 3 cm.

A polarization transformer 20 based on Polarization Maintaining Fiber (PMF) has a typical birefringence of about 10-3. As this is much lower than in LiNbO3, a much longer length is required: 2.25m. By increasing the length even further, a higher spectral resolution can be achieved. However, typical DWDM component test applications would require a spectral resolution of the PDL and PMD measurement around 1...3pm. Therefore a PMF fiber length of more than 1000m would be required, which might not be applicable for some applications e.g. for price, volume and possibly stability reasons.

In a further preferred implementation, an 'artificial birefringent device' 200 is used as polarization transformer 20 creating enough delay between the two propagating polarization modes for very high spectral resolution. The incoming (linearly polarized) light is split up in the artificial birefringent device 200 and guided along two different paths having different path lengths with a length difference &Dgr;L. The artificial birefringent device 200 further provides the light returning from the two paths with orthogonal states of polarization. This can be done e.g. by splitting up the incoming light polarization dependent or by changing the state of polarization at least in one of the paths. After recombining the light returning from both paths, the state of polarization of the combined signal depends on the wavelength (or more accurately the frequency) of the optical signal in a deterministic, periodic way. By adjusting the length difference &Dgr;L the periodicity can be broadly varied.

Fig. 3 shows a first embodiment of the artificial birefringent device 200. The incoming (linearly polarized) light is split up by a beam splitter or fiber coupler 210 and guided along the two different paths. One (typically short) path returns the signal with its original polarization. A second path, which has a geometric length difference &Dgr;L, returns the signal in its orthogonal state of polarization, e.g. by providing a Faraday Mirror 220. After recombining the light of the first and the second path, the state of polarization of the combined signal depends on the wavelength of the optical signal.

Fig. 4 shows a further embodiment of an artificial birefringent device 200, preferably made of PMF components. The incoming (linearly polarized) light is split up by a polarization dependent beam splitter 250 into light beams having orthogonal states of polarization, guided along the two different paths with the length difference of &Dgr;L, and recombined with the still orthogonal states of polarization. The state of polarization of the combined signal again depends on the wavelength of the optical signal. In order to provide both paths with substantially the same optical powers, a polarizer 260 might be inserted before the polarization dependent beam splitter 250 in order to polarize the incoming light to 45° with respect to polarization states provided by the polarization dependent beam splitter 250.

The artificial birefringent device 200 allows creating an almost arbitrarily selectable delay difference between two signal fractions. The delay difference is defined by the length difference of the fibers &Dgr;L. For this setup Equation 2 changes to: &Dgr; &lgr; &Dgr; &agr; 1 &lgr; 2 2 &pgr; n &Dgr; L

where n represents the refractive index of the fiber. As an example, getting a PDL or PMD measurement resolution of 1 pm can be achieved by a length difference &Dgr;L=1.5m.


Anspruch[de]
System zur Messung eines polarisationsabhängigen Parameters einer zu testenden Einheit (Device Under Test, DUT) 30 bei einer ersten und einer davon verschiedenen zweiten Polarisation, wobei das System Folgendes aufweist: eine Lichtquelle (10) zum Bereitstellen eines optischen Anregungssignals mit einem Polarisationszustand bei variierenden Wellenlängen, ein Mittel (20) zum Umwandeln des Polarisationszustandes des von der Lichtquelle (10) eingegebenen optischen Anregungssignals an seinem Eingang in einen Polarisationszustand eines optischen Signals an seinem Ausgang auf deterministische Weise in Abhängigkeit von der Wellenlänge des optischen Anregungssignals und zum Einspeisen des optischen Signals an seinem Ausgang in die DUT (30), eine Empfangseinheit (40) zum Empfangen eines optischen Antwortsignals von der DUT (30) als Reaktion auf das eingegebene optische Anregungssignal, und eine Analyseeinheit (60) zum Analysieren empfangener optischer Antwortsignale für verschiedene Wellenlängen zum Ermitteln von Werten des polarisationsabhängigen Parameters der DUT (30),

dadurch gekennzeichnet, dass
das Mittel (20) eine Polarisationsumwandlungseinheit ist, die so gestaltet ist, dass der Polarisationszustand des in die DUT (30) eingespeisten optischen Signals beim Variieren der Wellenlänge des optischen Anregungssignals zwischen der ersten und der zweiten Polarisation wechselt.
System nach Anspruch 1, bei dem die Polarisationsumwandlungseinheit (20) zum Analysieren eines Satzes von vier Messpunkten mit verschiedenen Polarisationszuständen und die Lichtquelle (10) zum Bereitstellen des Satzes der Messpunkte in einem Wellenlängenbereich eingerichtet ist, der kleiner als die Wellenlängenauflösung für diese Messung ist. System nach Anspruch 1, bei dem die Polarisationsumwandlungseinheit (20) die Umwandlung der Polarisation in Abhängigkeit von der Wellenlänge unter Verwendung von Doppelbrechungseigenschaften bewirkt. System nach Anspruch 1, bei dem die Lichtquelle (10) so beschaffen ist, dass sie die Wellenlänge mit der Zeit variiert, und bei dem die Polarisationsumwandlungseinheit (20) so beschaffen ist, dass sie die Polarisation in Abhängigkeit von der durch die Lichtquelle (10) bewirkten zeitlichen Änderung der Wellenlänge mit der Zeit variiert. Verfahren zur Messung eines polarisationsabhängigen Parameters einer zu testenden optischen Einheit - DUT - (30) bei einer ersten und bei einer davon verschiedenen zweiten Polarisation, wobei das Verfahren folgende Schritte aufweist: (a) Bereitstellen eines optischen Anregungssignals mit einem Polarisationszustand bei variierenden Wellenlängen, (b) Verwenden eines Mittels (20) zum Umwandeln des Polarisationszustandes des an seinem Eingang eingegebenen optischen Anregungssignals auf deterministische Weise in Abhängigkeit von der Wellenlänge des optischen Anregungssignals und zum Einspeisen des optischen Signals an seinem Ausgang in die DUT (30), (c) Empfangen eines optischen Antwortsignals von der DUT (30) als Reaktion auf das eingegebene optische Anregungssignals, und (d) Analysieren empfangener optischer Antwortsignale zum Ermitteln von Werten des polarisationsabhängigen Parameters der DUT (30), dadurch gekennzeichnet, dass

das Mittel (20) eine Polarisationsumwandlungseinheit ist, die so gestaltet ist, dass der Polarisationszustand des in die DUT (30) eingespeisten optischen Signals beim Variieren der Wellenlänge des optischen Anregungssignals zwischen der ersten und der zweiten Polarisation wechselt.
Verfahren nach Anspruch 5, bei dem: in Schritt (a) das optische Anregungssignal mit einer zeitlichen Variation der Wellenlänge bereitgestellt wird, und in Schritt (b) der Polarisationszustand des optischen Anregungssignals in Abhängigkeit von der durch Schritt (a) bereitgestellten zeitlichen Variation mit der Zeit variiert. Verfahren nach Anspruch 5 oder 6, bei dem in Schritt (a) die Wellenlänge des optischen Anregungssignals derart variiert wird, dass das Signal keinen Polarisationseigenzustand der Polarisationsumwandlungseinheit (Principle State of the Polarization of the polarization translator) (20) erreicht, sodass das Ausgangssignal der Polarisationsumwandlungseinheit (20) auf deterministische Weise einer Bahn auf der Poincaré-Kugel folgt. Verfahren nach einem der Ansprüche 5 bis 7, bei dem in Schritt (d) mehrere durch die Wellenlänge und den Polarisationszustand definierte Messpunkte gemeinsam analysiert werden, um einen Wert des polarisationsabhängigen Parameters der DUT (30) zu ermitteln. Verfahren nach Anspruch 8, bei dem der Wellenlängenbereich für solche gemeinsam zu analysierende Messpunkte so ausgewählt wird, dass der eine Wert des polarisationsabhängigen Parameters der DUT (30) in diesem Wellenlängenbereich im Wesentlichen als konstant angesehen werden kann. Verfahren nach einem der Ansprüche 5 bis 9, bei dem Schritt (d) mindestens einen der folgenden Algorithmen ausführt: Interpolation benachbarter Messpunkte, Kombinieren von vier Messpunkten unter Verwendung der Müllerschen Matrixanalyse oder Kombinieren von zwei Messpunkten unter Verwendung der Jones'schen Matrixanalyse. Verfahren nach einem der Ansprüche 5 bis 10, bei dem der polarisationsabhängige Parameter einer der folgenden Parameter ist: polarisationsabhängiger Verlust (polarization dependent loss), polarisationsabhängige Gruppenlaufzeit (polarization dependent group delay), differenzielle Gruppenlaufzeit (differential group delay) oder Polarisationsmodendispersion (polarization mode dispersion).
Anspruch[en]
A system for measuring a polarization dependent parameter of an optical device under test - DUT - (30), at a first and a different second polarization, comprising : an optical source (10) adapted for providing an optical stimulus signal of a polarization state at variable wavelengths, a means (20) being adapted for translating the polarization state of the optical stimulus signal applied from the optical source (10) at its input into a polarization state of an optical signal at its output in a deterministic way dependent on the wavelength of the optical stimulus signal, and for launching the optical signal at its output into the DUT (30), a receiving unit (40) adapted for receiving an optical response signal from the DUT (30) to the applied optical stimulus signal, and an analyzing unit (60) adapted for analyzing received optical response signals for different wavelengths for determining values of the polarization dependent parameter of the DUT (30), characterized in that the means (20) is a polarization translator which is configured such that the polarization state of the optical signal launched into the DUT (30) changes between the first and the second polarization upon variation of the wavelength of the optical stimulus signal. The system of claim 1, wherein the polarization translator (20) is adapted for analyzing a set of four measurement points with different polarization states and wherein the optical source (10) is adapted for providing the set of said measurement points in a wavelength range being smaller than the wavelength resolution for that measurement. The system of claim 1, wherein the polarization translator (20) provides the translation of the polarization dependent on the wavelength by using birefringent properties. The system of claim 1, wherein the optical source (10) is adapted to provide a variation of the wavelength over the time, and the polarization translator (20) is adapted to provide a variation of the polarization over the time in accordance with the variation of the wavelength over the time provided by the optical source (10). A method for measuring a polarization dependent parameter of an optical device under test -DUT-(30) at a first and a different second polarization, comprising the steps of: (a) providing an optical stimulus signal of a polarization state at variable wavelengths, (b) using a means (20) for translating the polarization state of the optical stimulus signal applied at its input into a polarization state of an optical signal at its output in a deterministic way dependent on the wavelength of the optical stimulus signal, and for launching the optical signal at its output into the DUT (30), (c) receiving an optical response signal from the DUT (30) to the applied optical stimulus signal, and (d) analyzing received optical response signals for determining values of the polarization dependent parameter of the DUT (30), characterized in that the means (20) is a polarization translator which is configured such that the polarization state of the optical signal launched into the DUT (30) changes between the first and the second polarization upon variation of the wavelength of the optical stimulus signal. The method of claim 5, wherein: in step (a) the optical stimulus signal is provided with a variation of the wavelength over the time, and in step (b) the polarization state of the optical stimulus signal is varied over the time in accordance with the variation of the wavelength over the time provided by step (a). The method of claim 5 or 6, wherein in step (a) the wavelength of the optical stimulus signal is varied in a way that it does not hit a Principle State of the Polarization of the polarization translator (20), so that the output signal of the polarization translator (20) will follow a trajectory on the Poincare Sphere in a deterministic way. The method of any one of the claims 5-7, wherein in step (d) several measurement points measurement points defined by the wavelength and the polarization state are analyzed together for determining one value of the polarization dependent parameter of the DUT (30). The method of claim 8, wherein the wavelength range for such measurement points to be analyzed together is selected so that the one value of the polarization dependent parameter of the DUT (30) can be considered as substantially constant in that wavelength range. The method of any one of the claims 5-9, wherein step (d) executes at least one of the algorithms: interpolation of neighboring measurement points, combining four measurement points using the Mueller Matrix analysis, or combining two measurement points using the Jones Matrix analysis. The method of any one of the claims 5-10, wherein the polarization dependent parameter is one of polarization dependent loss, polarization dependent group delay, differential group delay, or polarization mode dispersion.
Anspruch[fr]
Système de mesure d'un paramètre, dépendant de la polarisation, d'un dispositif optique en cours de test - DUT - (30) à une première polarisation et à une deuxième polarisation différente, comprenant: une source optique (10) apte à envoyer un signal de stimulus optique d'un état de polarisation à des longueurs d'ondes variables, un moyen (20) apte à translater l'état de polarisation du signal de stimulus optique appliqué, à son entrée, par la source optique (10) en un état de polarisation d'un signal optique à sa sortie, d'une manière déterministe qui dépend de la longueur d'onde du signal de stimulus optique, et à lancer dans le DUT (30) le signal optique présent à sa sortie, une unité réceptrice (40) apte à recevoir du DUT (30) un signal optique de réponse au signal de stimulus optique appliqué, et une unité d'analyse (60) apte à analyser des signaux optiques reçus de réponse pour différentes longueurs d'ondes afin de déterminer des valeurs du paramètre dépendant de la polarisation du DUT (30), caractérisé en ce que le moyen (20) est un translateur de polarisation qui est configuré d'une manière telle que l'état de polarisation du signal optique lancé dans le DUT (30) varie entre la première et la deuxième polarisation lors d'une variation de la longueur d'onde du signal de stimulus optique. Système selon la revendication 1, dans lequel le translateur (20) de polarisation est apte à analyser un ensemble de quatre points de mesure à différents états de polarisation, et dans lequel la source optique (10) est apte à réaliser l'ensemble desdits points de mesure dans une plage de longueurs d'ondes plus petite que la résolution de longueur d'onde pour cette mesure. Système selon la revendication 1, dans lequel le translateur (20) de polarisation réalise la translation de la polarisation qui dépend de la longueur d'onde en utilisant des propriétés biréfringentes. Système selon la revendication 1, dans lequel la source optique (10) est apte à réaliser une variation de la longueur d'onde au cours du temps, et le translateur (20) de polarisation est apte à réaliser une variation de la polarisation au cours du temps en fonction de la variation de la longueur d'onde au cours du temps que la source optique (10) réalise. Procédé de mesure d'un paramètre, dépendant de la polarisation, d'un dispositif optique en cours de test - DUT - (30) à une première polarisation et à une deuxième polarisation différente, comprenant les étapes consistant à: (a) fournir un signal de stimulus optique d'un état de polarisation à des longueurs d'ondes variables, (b) utiliser un moyen (20) pour translater l'état de polarisation du signal de stimulus optique appliqué à son entrée en un état de polarisation d'un signal optique à sa sortie d'une manière déterministe qui dépend de la longueur d'onde du signal de stimulus optique, et pour lancer dans le DUT (30) le signal optique présent à sa sortie, (c) recevoir du DUT (30) un signal optique de réponse au signal de stimulus optique appliqué, et (d) analyser des signaux optiques reçus de réponse afin de déterminer des valeurs du paramètre dépendant de la polarisation du DUT (30), caractérisé en ce que le moyen (20) est un translateur de polarisation qui est configuré d'une manière telle que l'état de polarisation du signal optique lancé dans le DUT (30) varie entre la première et la deuxième polarisation lors d'une variation de la longueur d'onde du signal de stimulus optique. Procédé selon la revendication 5, dans lequel: à l'étape (a), une variation de la longueur d'onde est communiquée au signal de stimulus optique au cours du temps, et à l'étape (b), l'état de polarisation du signal de stimulus optique varie au cours du temps en fonction de la variation de la longueur d'onde au cours du temps communiquée par l'étape (a). Procédé selon la revendication 5 ou 6, dans lequel, à l'étape (a), une variation de la longueur d'onde est communiquée au signal de stimulus optique d'une manière qui ne perturbe pas un Etat de Polarisation de Principe du translateur (20) de polarisation, de sorte que le signal de sortie du translateur (20) de polarisation suit d'une manière déterministe une trajectoire sur la sphère de Poincaré. Procédé selon l'une quelconque des revendications 5 à 7, dans lequel, à l'étape (d), plusieurs points de mesure définis par la longueur d'onde et l'état de polarisation sont analysés ensemble pour déterminer une valeur du paramètre dépendant de la polarisation du DUT (30). Procédé selon la revendication 8, dans lequel la plage des longueurs d'ondes de ces points de mesure à analyser ensemble est sélectionnée d'une manière telle que la valeur, précisée dans la revendication précédente, du paramètre dépendant de la polarisation du DUT (30) peut être considérée comme sensiblement constante dans cette plage de longueurs d'ondes. Procédé selon l'une quelconque des revendications 5 à 9, dans lequel l'étape (d) exécute au moins l'un des algorithmes suivants: interpolation de points voisins de mesure, combinaison de quatre points de mesure en utilisant l'analyse par Matrice de Mueller, ou combinaison de deux points de mesure en utilisant l'analyse par Matrice de Jones. Procédé selon l'une quelconque des revendications 5 à 10, dans lequel le paramètre dépendant de la polarisation est, soit une perte dépendant de la polarisation, soit un retard de groupe dépendant de la polarisation, soit un retard différentiel de groupe, soit une dispersion de mode de polarisation.






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