Iec 60793 1 45 2001

Fibres optiques –Partie 1-45: Méthodes de mesure et procédures d'essai – Diamètre du champ de mode Optical fibres – Part 1-45: Measurement methods and test procedures – Mode field diamet

Source lumineuse

For methods A, B, and C, it is essential to utilize a suitable source of coherent or incoherent light, such as a semiconductor laser or a sufficiently powerful filtered white light source The light source must generate adequate radiation at the desired wavelength and maintain stable intensity for a sufficient duration to facilitate accurate measurements.

If needed, a monochromator or interference filters can be used for wavelength selection The wavelength of the source must be specified in the particular specifications The full width at half maximum (FWHM) of the source should be 10 nm or less, unless otherwise specified.

Voir l'annexe D pour la méthode D.

Système optique d'entrée

For methods A, B, and C, it is acceptable to use an optical lens system or a launch fiber to excite the test fiber It is advisable that the power coupled into the test fiber remains relatively insensitive to the position of the fiber's input face This can be achieved by employing an injection beam that allows for both spatial and angular saturation of the input face.

When using a butt splice, it is essential to employ an index-matching material between the launch fiber and the test fiber to prevent interference phenomena The coupling must remain stable throughout the duration of the test.

Voir l'annexe D pour la méthode D.

LICENSED TO MECON Limited - RANCHI/BANGALORE FOR INTERNAL USE AT THIS LOCATION ONLY, SUPPLIED BY BOOK SUPPLY BUREAU.

This section of IEC 60793 references several normative documents that are integral to its provisions For dated references, any amendments or revisions to these publications are not applicable However, parties involved in agreements based on this standard are encouraged to consider the latest editions of the referenced documents In the case of undated references, the most recent edition of the cited normative document is applicable Additionally, IEC and ISO members keep updated registers of valid International Standards.

IEC 60793-1-40, Optical fibres – Part 1-40: Measurement methods and test procedures –

IEC 60793-2:1998, Optical fibres – Part 2: Product specifications

Method A, direct far-field scan, is the reference test method (RTM), which shall be the one used to settle disputes.

The following apparatus is common to all measurement methods Annexes A, B, C and D include layout drawings and other equipment requirements for each of the four methods, respectively.

For methods A, B, and C, it is essential to utilize an appropriate light source, which can be either coherent or non-coherent, such as a semiconductor laser or a powerful filtered white light source The chosen source must emit adequate radiation at the specified wavelength(s) and maintain stable intensity over a duration sufficient for accurate measurements.

A monochromator or interference filter(s) may be used, if required, for wavelength selection.

The detailed specification must include the wavelength of the source, and the full width half maximum (FWHM) spectral line width should not exceed 10 nm, unless stated otherwise.

Method A, B, and C utilize an optical lens system or fiber pigtail to excite the specimen It is essential to ensure that the power coupled into the specimen remains largely unaffected by the position of its input end face This can be achieved by employing a launch beam that spatially and angularly overfills the input end face.

To ensure stable coupling during measurements, use index-matching material between the fiber pigtail and the specimen when employing a butt splice, as this will help prevent interference effects.

Dispositif de positionnement d'entrée

Ensure a mechanism is in place for accurately positioning the sample's entry point relative to the light source Examples include using x-y-z micropositioner stages or mechanical coupling devices such as connectors, vacuum splices, and three-pin splices It is crucial that the fiber's position remains stable throughout the measurement process.

Extracteur de modes de gaine

Utiliser un dispositif d'extraction de modes de gaine Dans certains cas, c'est le revêtement de la fibre qui assure cette fonction.

Filtre des modes d'ordre supérieur

To prevent the propagation of higher-order modes in wavelengths exceeding the cutoff wavelength of the tested fiber, a single loop with a radius of approximately 30 mm is typically sufficient.

Dispositif de positionnement de sortie

Ensure an appropriate setup for aligning the output end face of the fiber to allow precise axial adjustment This alignment is crucial for focusing the measurement wavelength correctly on the scanning detector plane Such coupling may involve the use of lenses or a mechanical connector to a detector's input fiber.

To effectively locate the fiber at a fixed distance from the openings or detector, it is advisable to use a side-view microscope or a camera equipped with a reticle In some cases, a longitudinal adjustment may be sufficient if the fiber is held in the lateral plane by a device like a suction mandrel, depending primarily on the size of the light detector.

Dispositif optique de sortie

Détecteur

Calculateur

Use a calculator to perform operations such as device checks, intensity measurements, and data processing to obtain final results For detailed operations, refer to the appropriate appendices: A, B, C, or D.

Longueur de l'échantillon à l’essai

Pour les méthodes A, B et C, la longueur de l'échantillon à l’essai doit être une longueur connue, généralement de 2 m ± 0,2 m, de fibre unimodale.

For the D method, RODT, the sample must be long enough to extend beyond the dead zone of the RODT, with both ends accessible, as outlined in the IEC 60793-1-40 backscattering test method.

To ensure accurate measurements, it is essential to properly position the input end of the specimen to the light source This can be achieved using x-y-z micropositioner stages or mechanical coupling devices like connectors, vacuum splices, and three-rod splices Maintaining a stable position of the fiber throughout the measurement process is crucial for reliable results.

Use a device that extracts cladding modes Under some circumstances the fibre coating will perform this function.

To eliminate high-order propagating modes in the wavelength range equal to or exceeding the specimen's cut-off wavelength, employing a one-turn bend with a radius of 30 mm on the fiber is typically effective.

To ensure precise axial alignment of the fiber output end face, it is essential to implement an effective method that focuses the scan pattern on the scanning detector's plane at the measurement wavelength This alignment can be achieved through the use of lenses or by employing a mechanical connector to a detector pigtail.

To effectively locate the fiber at a fixed distance from the apertures or detectors, utilize tools like a side-viewing microscope or a camera equipped with a crosshair In cases where the fiber is secured laterally by a device such as a vacuum chuck, it may only be necessary to implement longitudinal adjustments, depending primarily on the dimensions of the light detector.

See the appropriate annex: A, B, C or D.

Utilize a computer to manage device operations, measure intensity, and analyze data to achieve final outcomes For specific information, refer to the relevant annexes: A, B, C, or D.

For methods A, B and C, the specimen shall be a known length, typically 2 m ± 0,2 m of single- mode fibre.

For method D, OTDR, it is essential that the sample length surpasses the dead zone of the OTDR and that both ends are accessible, as outlined in the backscatter test method IEC 60793-1-40.

Surface d'extrémité de l'échantillon à l’essai

Préparer une surface plane, perpendiculaire à l'axe de la fibre, à l'extrémité d'entrée et à l'extrémité de sortie de l'échantillon à l’essai.

Voir respectivement les annexes A, B, C et D pour les méthodes A, B, C et D.

The fundamental equations for calculating the DCM for methods A, B, and C are provided below For additional calculations, please refer to the relevant appendices: A, B, C, or D Sample data sets for methods A, B, and C can be found in appendix E.

Méthode A – Exploration directe du champ lointain

L'équation suivante définit le DCM pour la méthode A en termes de champ électromagnétique émis à partir de l'extrémité de l'échantillon à l’essai.

To calculate the DCM using data from far-field exploration and the evaluation of the Petermann II integral, one must consider the intensity distribution in the far field.

2W 0 est le DCM, en àm;

The far-field intensity distribution, denoted as P F (θ), is influenced by the measurement wavelength, λ, expressed in ångströms (àm) Additionally, θ represents the angle measured in the far field relative to the fiber axis.

The integration limits range from zero to \(\frac{\pi}{2}\); however, it is understood that the integrands approach zero as the integration variable increases, allowing for the practical truncation of the integrals.

NOTE 2 P F est la F 2 ( θ ) dans les publications de l’UIT-T.

The far-field method for determining the DCM of a single-mode fiber involves a two-step procedure The first step is to measure the radiation pattern of the fiber in the far field The second step utilizes a mathematical approach based on Petermann II's definition of the far field to calculate the mode field from the far-field data, as outlined in the aforementioned equation.

Annex E presents sample data and calculated values for 2W 0, enabling the verification of the numerical evaluation of the Petermann II integral The sample data is expressed as the symmetrized power by means of deviations, P F (θ), as a function of the angle, θ.

Prepare a flat end face, orthogonal to the fibre axis, at the input and output ends of each specimen.

See annex A, B, C and D for methods A, B, C and D, respectively.

The basic equations for calculating MFD by methods A, B and C are given below For additional calculations, see the appropriate annex: A, B, C or D Sample data sets for methods

A, B and C are included in annex E.

7.1 Method A – Direct far-field scan

The following equation defines the MFD for method A in terms of the electromagnetic field emitted from the end of the specimen.

Calculate the MFD by scanning the far-field data and evaluating the Petermann II integral, which is defined from the far-field intensity distribution:

2W 0 is the MFD in àm;

P F (θ) is the far-field intensity distribution; λ is the wavelength of measurement in àm; θ is the angle in the far-field measurement from the axis of the fibre.

The integration limits range from zero to \(\frac{\pi}{2}\), but it is important to note that the integrands tend to zero as the argument increases, allowing for practical truncation of the integrals.

NOTE 2 P F is the F 2 ( θ ) in ITU-T publications.

The far-field method for obtaining the MFD of a single-mode fibre is a two-step procedure.

To begin, assess the far-field radiation pattern of the fiber Next, apply a mathematical method grounded in the Petermann II far-field definition to derive the mode field from the far-field data, as outlined in equation (1).

Annex E offers sample data and computed values for 2W 0, allowing for the verification of the numerical evaluation of the Petermann II Integral The data is presented as the folded power, P F (θ), which varies with the angle, θ.

Méthode B – Ouverture variable en champ lointain

Les équations suivantes définissent le DCM pour la méthode B en termes de champ électromagnétique émis à partir de l'extrémité de l'échantillon à l’essai.

Calculer le DCM, 2W 0 , comme suit:

2W 0 est le DCM, en àm; λ est la longueur d'onde de mesure, en àm;

D est la distance entre l'ouverture et la fibre, en mm; a(x) est la fonction de transmission de l'ouverture complémentaire, calculée comme:

P(x) est la puissance mesurée à travers une ouverture de rayon, x, ou de demi-angle, θ;

P(max) est la puissance maximale, supposant une ouverture infinie; x est le rayon d'ouverture, calculé comme: x = D tan(θ) (4) ó D est la distance entre l'ouverture et la fibre, en mm.

The mathematical equivalence of equations (1) and (2) holds true under the small angle approximation, θ Within this framework, equation (2) can be derived from equation (1) through integration Additionally, there exists another equivalent expression for equation (2).

2W 0 est le DCM, en àm; a(θ) est la fonction de l'ouverture complémentaire, calculée suivant:

P(θ) est la puissance à travers l'ouverture la plus grande;

P(max) est la puissance maximale, supposant une ouverture infinie.

The variable aperture method in far-field for calculating the DCM of a single-mode fiber involves a two-step procedure The first step measures the two-dimensional far-field distribution by assessing the power passing through apertures of varying sizes The second step employs a mathematical procedure to compute the DCM from the far-field data.

7.2 Method B – Variable aperture in the far field

The following equations define the MFD for method B in terms of the electromagnetic field emitted from the end of the specimen.

Calculate the MFD, 2W 0 , as follows:

2W 0 is the MFD, in àm; λ is the wavelength of measurement, in àm;

D is the distance between the aperture and the fibre, in mm; a(x) is the complementary aperture transmission function, calculated as

P(x) is the power measured through an aperture of radius, x, or half angle, θ;

P(max) is the maximum power, assuming an infinite aperture; x is the aperture radius, calculated as x = D tan(θ) (4) where D is the distance between the aperture and the fibre, in mm.

The equivalence of equations (1) and (2) holds true when approximating small angles, θ In this context, equation (2) can be derived from equation (1) through integration Additionally, there exists another equivalent expression for equation (2).

2W 0 is the MFD, in àm; a(θ) is the complementary aperture function, calculated as

P(θ) is the power through the largest aperture;

P(max) is the maximum power, assuming an infinite aperture.

The variable aperture far-field method for determining the mode field diameter (MFD) of a single-mode fiber involves a two-step process Initially, the two-dimensional far-field pattern is measured by assessing the power transmitted through a range of apertures of different sizes Subsequently, a mathematical procedure is employed to derive the MFD from the collected far-field data.

The mathematical foundation for calculating the DCM is based on Petermann II's definition of the far field derived from equation (1) The mathematical equivalence of equations (1) and (3) holds true under the small angle approximation, θ Equation (5) can be obtained from equation (1) through integration.

Méthode C – Exploration en champ proche

L'équation suivante définit le DCM pour la méthode C en termes de champ électromagnétique émis à partir de l'extrémité de l'échantillon à l’essai.

Calculer le DCM à partir de la répartition de l'intensité en champ proche mesurée, au moyen de l'intégrale suivante:

2W 0 est le DCM, en àm; r est la coordonnộe radiale, en àm; f 2 (r) est la répartition de l'intensité en champ proche.

The upper limit of integration extends to infinity; however, it is understood that the integrands approach zero as the integration variable increases, allowing for practical truncation of the integrals A smoothing algorithm can be employed for the calculation of the derivative.

The near-field exploration method for determining the DCM of a single-mode fiber involves a two-step procedure The first step is to measure the near-field radiation pattern of the fiber The second step employs a mathematical procedure to calculate the mode field from the near-field data.

The mathematical foundation for calculating the DCM is based on Petermann II's definition derived from equation (1) The mathematical equivalence of equations (1) and (5) holds true under the small angle approximation, θ Within this approximation, the near field, f(r), and the far field, F(θ), constitute a Hankel pair Utilizing the Hankel transformation allows for the transition between equation (1) and equation (7), and vice versa.

Informations à fournir pour chaque mesure

Relever les informations suivantes pour chaque mesure:

– date et titre de l'essai;

– longueur d'onde de la source optique;

– diamốtre(s) du champ de mode, en àm.

Light source

For methods A, B, and C, it is essential to utilize an appropriate light source, either coherent or non-coherent, such as a semiconductor laser or a powerful filtered white light source The chosen source must emit adequate radiation at the specified wavelength(s) and maintain stable intensity over a duration sufficient for accurate measurements.

A monochromator or interference filter(s) may be used, if required, for wavelength selection.

The detailed specification must include the wavelength of the source, and the full width half maximum (FWHM) spectral line width should not exceed 10 nm, unless stated otherwise.

Input optics

Method A, B, and C utilize an optical lens system or fiber pigtail to excite the specimen It is essential that the power coupled into the specimen remains largely unaffected by the position of its input end face Achieving this can be done by employing a launch beam that spatially and angularly overfills the input end face.

To ensure stable coupling during measurements, use index-matching material between the fiber pigtail and the specimen when employing a butt splice, as this will help prevent interference effects.

Ensure a mechanism is in place to accurately position the sample's entry point relative to the light source Examples include using x-y-z micropositioner stages or mechanical coupling devices such as connectors, vacuum splices, and three-pin splices It is crucial that the fiber's position remains stable throughout the measurement process.

4.4 Extracteur de modes de gaine

Utiliser un dispositif d'extraction de modes de gaine Dans certains cas, c'est le revêtement de la fibre qui assure cette fonction.

4.5 Filtre des modes d'ordre supérieur

To prevent the propagation of higher-order modes in wavelengths exceeding the cutoff wavelength of the tested fiber, a single loop with a radius of approximately 30 mm around the fiber is typically sufficient.

4.6 Dispositif de positionnement de sortie

Ensure an appropriate setup for aligning the output end face of the fiber to allow precise axial adjustment, so that at the measurement wavelength, the scan is properly focused on the scanning detector plane This coupling may involve the use of lenses or a mechanical connector to a fiber leading to the detector.

To effectively locate the fiber at a fixed distance from the openings or detector, it is advisable to use a side-view microscope or a camera equipped with a reticle In some cases, a longitudinal adjustment may be sufficient if the fiber is held in the lateral plane by a device like a suction mandrel, depending primarily on the size of the light detector.

Use a calculator to perform operations such as device checks, intensity measurements, and data processing to obtain final results For detailed operations, refer to the appropriate appendices: A, B, C, or D.

Pour les méthodes A, B et C, la longueur de l'échantillon à l’essai doit être une longueur connue, généralement de 2 m ± 0,2 m, de fibre unimodale.

For method D, RODT, the sample must be long enough to extend beyond the dead zone of the RODT, with both ends accessible, as outlined in the IEC 60793-1-40 backscattering test method.

Input positioner

To ensure accurate measurements, it is essential to properly position the input end of the specimen to the light source This can be achieved using x-y-z micropositioner stages or mechanical coupling devices, including connectors, vacuum splices, and three-rod splices Maintaining a stable position of the fiber throughout the measurement process is crucial for reliable results.

Cladding mode stripper

Use a device that extracts cladding modes Under some circumstances the fibre coating will perform this function.

High-order mode filter

To eliminate high-order propagating modes in the wavelength range equal to or greater than the specimen's cut-off wavelength, a one-turn bend with a radius of 30 mm on the fiber is typically effective.

Output positioner

To ensure precise axial alignment of the fiber output end face, it is essential to implement an effective method that focuses the scan pattern on the scanning detector's plane at the measurement wavelength This alignment can be achieved through the use of lenses or by employing a mechanical connector to a detector pigtail.

To accurately locate the fiber at a fixed distance from the apertures or detectors, utilize tools like a side-viewing microscope or a camera equipped with a crosshair In cases where the fiber is secured laterally by a device such as a vacuum chuck, it may only be necessary to implement longitudinal adjustments, depending primarily on the dimensions of the light detector.

Output optics

Detector

Computer

Utilize a computer to manage apparatus control, conduct intensity measurements, and process data to achieve final results For specific information, refer to the relevant annexes: A, B, C, or D.

Specimen length

For methods A, B and C, the specimen shall be a known length, typically 2 m ± 0,2 m of single- mode fibre.

For method D, OTDR, it is essential that the sample length surpasses the dead zone of the OTDR and that both ends are accessible, in accordance with the backscatter test method IEC 60793-1-40.

5.2 Surface d'extrémité de l'échantillon à l’essai

Préparer une surface plane, perpendiculaire à l'axe de la fibre, à l'extrémité d'entrée et à l'extrémité de sortie de l'échantillon à l’essai.

Voir respectivement les annexes A, B, C et D pour les méthodes A, B, C et D.

The fundamental equations for calculating the DCM for methods A, B, and C are provided below For additional calculations, please refer to the relevant appendices: A, B, C, or D Sample data sets for methods A, B, and C can be found in Appendix E.

7.1 Méthode A – Exploration directe du champ lointain

L'équation suivante définit le DCM pour la méthode A en termes de champ électromagnétique émis à partir de l'extrémité de l'échantillon à l’essai.

To calculate the DCM using data from far-field exploration and the evaluation of the Petermann II integral, one must consider the intensity distribution in the far field.

The far-field intensity distribution, denoted as P F (θ), is influenced by the measurement wavelength, λ, expressed in ångströms (àm) Additionally, θ represents the angle measured in the far field relative to the fiber axis.

The integration limits range from zero to \(\frac{\pi}{2}\); however, it is understood that the integrands approach zero as the integration variable increases, allowing for the practical truncation of the integrals.

NOTE 2 P F est la F 2 ( θ ) dans les publications de l’UIT-T.

The far-field method for determining the DCM of a single-mode fiber involves a two-step procedure The first step is to measure the radiation pattern of the fiber in the far field The second step utilizes a mathematical approach based on Petermann II's definition of the far field to calculate the mode field from the far-field data, as outlined in the aforementioned equation.

Annex E presents sample data and calculated values for 2W 0, enabling the verification of the numerical evaluation of the Petermann II integral The sample data is expressed as the symmetrized power by means of deviations, P F (θ), as a function of the angle, θ.

Specimen end face

Prepare a flat end face, orthogonal to the fibre axis, at the input and output ends of each specimen.

See annex A, B, C and D for methods A, B, C and D, respectively.

The basic equations for calculating MFD by methods A, B and C are given below For additional calculations, see the appropriate annex: A, B, C or D Sample data sets for methods

A, B and C are included in annex E.

Method A – Direct far-field scan

The following equation defines the MFD for method A in terms of the electromagnetic field emitted from the end of the specimen.

Calculate the MFD by scanning the far-field data and evaluating the Petermann II integral, which is defined from the far-field intensity distribution:

2W 0 is the MFD in àm;

P F (θ) is the far-field intensity distribution; λ is the wavelength of measurement in àm; θ is the angle in the far-field measurement from the axis of the fibre.

The integration limits range from zero to \(\frac{\pi}{2}\), but it is important to note that the integrands tend to zero as the argument increases, allowing for the practical truncation of the integrals.

NOTE 2 P F is the F 2 ( θ ) in ITU-T publications.

The far-field method for obtaining the MFD of a single-mode fibre is a two-step procedure.

To begin, assess the far-field radiation pattern of the fiber Next, apply a mathematical method grounded in the Petermann II far-field definition to derive the mode field from the far-field data, as outlined in equation (1).

Annex E offers sample data and computed values for 2W 0, allowing for the verification of the numerical evaluation of the Petermann II Integral The data is presented as the folded power, P F (θ), which varies with the angle, θ.

7.2 Méthode B – Ouverture variable en champ lointain

Les équations suivantes définissent le DCM pour la méthode B en termes de champ électromagnétique émis à partir de l'extrémité de l'échantillon à l’essai.

Calculer le DCM, 2W 0 , comme suit:

2W 0 est le DCM, en àm; λ est la longueur d'onde de mesure, en àm;

D est la distance entre l'ouverture et la fibre, en mm; a(x) est la fonction de transmission de l'ouverture complémentaire, calculée comme:

P(x) est la puissance mesurée à travers une ouverture de rayon, x, ou de demi-angle, θ;

P(max) est la puissance maximale, supposant une ouverture infinie; x est le rayon d'ouverture, calculé comme: x = D tan(θ) (4) ó D est la distance entre l'ouverture et la fibre, en mm.

The mathematical equivalence of equations (1) and (2) holds true under the small angle approximation, θ Within this framework, equation (2) can be derived from equation (1) through integration Additionally, there exists an alternative expression for equation (2).

2W 0 est le DCM, en àm; a(θ) est la fonction de l'ouverture complémentaire, calculée suivant:

P(θ) est la puissance à travers l'ouverture la plus grande;

P(max) est la puissance maximale, supposant une ouverture infinie.

The variable aperture method in far-field for calculating the DCM of a single-mode fiber involves a two-step procedure The first step is to measure the two-dimensional far-field distribution, which represents the power passing through apertures of varying sizes The second step is a mathematical process that calculates the DCM from the far-field data.

Method B – Variable aperture in the far field

The following equations define the MFD for method B in terms of the electromagnetic field emitted from the end of the specimen.

Calculate the MFD, 2W 0 , as follows:

2W 0 is the MFD, in àm; λ is the wavelength of measurement, in àm;

D is the distance between the aperture and the fibre, in mm; a(x) is the complementary aperture transmission function, calculated as

P(x) is the power measured through an aperture of radius, x, or half angle, θ;

P(max) is the maximum power, assuming an infinite aperture; x is the aperture radius, calculated as x = D tan(θ) (4) where D is the distance between the aperture and the fibre, in mm.

The mathematical equivalence of equations (1) and (2) holds true when approximating small angles, θ In this context, equation (2) can be derived from equation (1) through integration Additionally, there exists another equivalent expression for equation (2).

2W 0 is the MFD, in àm; a(θ) is the complementary aperture function, calculated as

P(θ) is the power through the largest aperture;

P(max) is the maximum power, assuming an infinite aperture.

The variable aperture far-field method for determining the mode field diameter (MFD) of a single-mode fiber involves a two-step process Initially, the two-dimensional far-field pattern is measured by assessing the power transmitted through a range of apertures of different sizes Subsequently, a mathematical procedure is employed to derive the MFD from the collected far-field data.

The mathematical foundation for calculating the DCM is based on Petermann II's definition of the far field derived from equation (1) The mathematical equivalence of equations (1) and (3) holds true under the small angle approximation, θ Equation (5) can be obtained from equation (1) through integration.

7.3 Méthode C – Exploration en champ proche

L'équation suivante définit le DCM pour la méthode C en termes de champ électromagnétique émis à partir de l'extrémité de l'échantillon à l’essai.

Calculer le DCM à partir de la répartition de l'intensité en champ proche mesurée, au moyen de l'intégrale suivante:

2W 0 est le DCM, en àm; r est la coordonnộe radiale, en àm; f 2 (r) est la répartition de l'intensité en champ proche.

The upper limit of integration extends to infinity; however, it is understood that the integrands approach zero as the integration variable increases, allowing for practical truncation of the integrals A smoothing algorithm can be employed for the calculation of the derivative.

The near-field exploration method for determining the DCM of a single-mode fiber involves a two-step procedure The first step is to measure the near-field radiation pattern of the fiber The second step employs a mathematical procedure to calculate the mode field from the near-field data.

The mathematical foundation for calculating the DCM is based on Petermann II's definition derived from equation (1) The mathematical equivalence of equations (1) and (5) holds true under the small angle approximation, θ Within this approximation, the near field, f(r), and the far field, F(θ), constitute a Hankel pair By utilizing the Hankel transform, one can transition from equation (1) to equation (7) and vice versa.

8.1 Informations à fournir pour chaque mesure

Relever les informations suivantes pour chaque mesure:

– date et titre de l'essai;

– longueur d'onde de la source optique;

– diamốtre(s) du champ de mode, en àm.

Les informations suivantes doivent être fournies sur demande:

– méthode de mesure utilisée: A, B, C ou D;

– type de source optique utilisée et largeur de raie spectrale (LMH);

The calculation of MFD is grounded in the Petermann II far-field definition as outlined in equation (1) The equivalence between equations (1) and (3) holds true under the small angle approximation, denoted by θ To derive equation (5), one must integrate equation (1).

Method C – Near-field scan

The following equation defines the MFD for method C in terms of the electromagnetic field emitted from the end of the specimen.

Calculate the MFD from the measured near-field intensity distribution, using the following integral:

2W 0 is the MFD, in àm; r is the radial coordinate, in àm; f 2 (r) is the near-field intensity distribution.

The upper limit of integration is set to infinity; however, it is important to note that the integrands tend to zero as the argument increases, allowing for practical truncation of the integrals Additionally, a smoothing algorithm can be employed to calculate the derivative effectively.

The near-field scan method for determining the mode field diameter (MFD) of a single-mode fiber involves a two-step process: initially, the radial near-field pattern is measured, followed by a mathematical calculation to derive the MFD from the collected near-field data.

The calculation of the MFD is grounded in the Petermann II definition as outlined in equation (1) The equivalence between equations (1) and (5) holds true when considering small angle approximations, θ In this context, both the near field, f(r), and the far field are analyzed.

F(θ), form a Hankel pair By means of the Hankel transformation it is possible to pass from equation (1) to equation (7), and reverse.

Information to be provided with each measurement

Report the following information with each measurement:

– date and title of measurement;

Information available upon request

The following information shall be available upon request:

– type of optical source used and its spectral width (FWHM);

– détails relatifs à la méthode de calcul;

– date du dernier étalonnage de l'équipement de mesure.

9 Informations à mentionner dans la spécification

La spécification particulière doit préciser les informations suivantes:

− critères de refus ou d'acceptation;

− toute divergence applicable par rapport à la procédure FOR INTERNAL USE AT THIS LOCATION ONLY, SUPPLIED BY BOOK SUPPLY BUREAU LICENSED TO MECON Limited - RANCHI/BANGALORE

– date of latest calibration of measurement equipment.

The detail specification shall specify the following information:

– type of fibre to be measured;

– any deviations to the procedure that apply FOR INTERNAL USE AT THIS LOCATION ONLY, SUPPLIED BY BOOK SUPPLY BUREAU LICENSED TO MECON Limited - RANCHI/BANGALORE

Prescriptions spécifiques à la méthode A – Diamètre du champ de mode par la technique de l'exploration directe en champ lointain

Cette annexe décrit l'appareillage en complément aux prescriptions de l’article 4.

La figure A.1 illustre un montage typique pour mesure par exploration directe en champ lointain.

Figure A.1 – Montage de mesure en champ lointain

A.1.1 Ensemble de détecteur à balayage – Système électronique de détection des signaux

To explore the distribution of intensities in the far field, a scanning mechanism should be employed, capable of operating in steps of 0.50° or finer to sweep the detector It is essential to align the fiber axis with the detector's rotation plane and ensure the fiber's end surface is centered with the scanning rotation A typical system may include a PIN photodiode operating in photovoltaic mode, amplified by a current preamplifier, with synchronous detection provided by a lock-in amplifier The detector should be positioned at least 10 mm from the fiber's end, ideally ensuring that the active area of the detector does not intercept a significant angle in the far field This can be achieved by placing the detector at a distance greater than \( \frac{2wb}{\lambda} \), where \( 2w \) is the expected DCM of the fiber being measured and \( b \) is the diameter of the detector's active area.

To achieve highly accurate measurements, a minimum dynamic range of 50 dB is essential, corresponding to maximum half-scan angles of 20° and 25° for B1 and B2 category fibers, respectively Reducing the dynamic range requirements or maximum half-scan angles may lead to significant errors For instance, limiting these values to 30 dB and 12.5° for B1 fibers, and 40 dB and 20° for B2 fibers, can result in a relative error greater than 1% in determining the DCM.

Requirements specific to method A – Mode field diameter by direct far-field scan

This annex describes apparatus in addition to the requirements set down in clause 4.

Figure A.1 illustrates a typical set-up for measurement by direct far-field scan.

Figure A.1 – Far-field measurement set

A.1.1 Scanning detector assembly – Signal detection electronics

Use a mechanism to scan the far-field intensity distribution Use a scanning device capable of

To achieve precise scanning of the detector, utilize 0.50° steps or finer while ensuring proper alignment of the fibre axis with the detector's rotation plane and the fibre end-face with the scan's center of rotation A typical setup may involve a PIN photodiode in photovoltaic mode, amplified by a current-input preamplifier, and employing synchronous detection via a lock-in amplifier It is crucial to position the detector at least 10 mm from the fibre end, ensuring that its active area does not cover a large angle in the far field To maintain this requirement, the detector should be placed at a distance greater than \( \frac{2wb}{\lambda} \), where \( 2w \) represents the expected mode field diameter (MFD) of the specimen and \( b \) is the diameter of the detector's active area.

For very accurate measurements, the minimum dynamic range of the measurement should be

50 dB This corresponds to a maximum scan half-angle of 20° and 25°, or greater, for category

Limiting the dynamic range and maximum scan half-angle for B1 and B2 fibres can lead to significant errors in measurement Specifically, setting these parameters to 30 dB and 12.5° for B1 fibres, and 40 dB and 20° for B2 fibres, may cause a relative error in the measurement of the mode field diameter (MFD) exceeding 1%.

Il convient qu'un système typique comprenne aussi un calculateur pour traiter les données en champ lointain.

Aligner dans le système la fibre, préparée conformément aux prescriptions décrites en 4.2, avec son extrémité de sortie alignée sur l'ensemble de détection pour assurer une puissance maximale.

Balayer le détecteur par échelons de 0,5°, également espacés, et enregistrer la puissance du détecteur.

Calculer une valeur de l'intégrale de Petermann II à partir des données enregistrées et l'utiliser pour calculer le DCM de la fibre, tel que décrit dans l'équation (1) et à l'article A.3.

A.3.1 Déterminer la courbe de puissance symétrisée par moyennes des écarts

La courbe de puissance symétrisée par moyennes des écarts pour 0 ≤ θ i = θ max est:

P F (θ i ) est la courbe de puissance symétrisée par moyennes des écarts;

P(θ–i ) est la puissance mesurée comme fonction de la position angulaire θ i (radians), indicé en i.

A.3.2 Calculer l'intégrale du numérateur ( T ) et l'intégrale du dénominateur ( B ) de l'équation (1)

To calculate the integrals of equation (1), it is essential to use an appropriate numerical integration method The following example demonstrates the rectangular method, although any other integration technique should achieve at least the same level of accuracy.

P f est la courbe de puissance symétrisée par moyennes des écarts; θ i est la position angulaire, indicé en i (radians); ó dθ = θ 1 – θ 0

A typical system should also include a computer to process the far-field data.

Align the fibre in the system, prepared as described in 4.2, with its output end aligned on the detector assembly for maximum power.

Scan the detector in 0,5° steps, equally spaced, and record the detector power.

Calculate a value of the Petermann II integral from the recorded data, and use it to compute the fibre MFD as described in equation (1), and in A.3.

The folded power curve for 0 ≤ θ i = θ max is

P F (θ i ) is the folded power curve;

P(θ–i) is the measured power as a function of the angular position, θ i (radians), indexed by i.

A.3.2 Compute the top ( T ) and bottom ( B ) integrals of equation (1)

Use an appropriate numerical integration technique to compute the integrals of equation (1).

The following is an example using the rectangular method Any other integration method shall be at least as accurate.

P f is the folded power curve; θ i is the angular position, indexed by i (radians); where dθ = θ 1 – θ 0

T est obtenue à partir de l'équation (A.2);

B est obtenue à partir de l'équation (A.3).

Refer to Table E.1 for the complete dataset on the sample as calculated in section A.3 This information is for internal use only at this location and is provided by the Book Supply Bureau, licensed to MECON Limited in Ranchi/Bangalore.

2W 0 is the MFD, in àm;

See table E.1 for a sample data set as calculated in A.3 FOR INTERNAL USE AT THIS LOCATION ONLY, SUPPLIED BY BOOK SUPPLY BUREAU LICENSED TO MECON Limited - RANCHI/BANGALORE

Prescriptions spécifiques à la méthode B – Diamètre du champ de mode par la technique de l'ouverture variable en champ lointain

Cette annexe décrit l'appareillage en complément aux prescriptions de l’article 4.

La figure B.1 illustre un montage typique pour la mesure par ouverture variable en champ lointain.

Figure B.1 – Montage de mesure par ouverture variable en champ lointain

B.1.1 Ensemble à ouvertures variables de sortie

To optimize the output power from the far-field radiation pattern of a fiber, position a device with circular transmission openings of varying sizes, such as a wheel with apertures, at a minimum distance of \(100 \frac{W_0}{\lambda}\) from the fiber Typically, these openings should be located between 20 mm and 50 mm from the fiber's end.

To enhance measurement accuracy, it is essential to center the openings relative to the radiation pattern, minimizing sensitivity to the angle formed with the fiber's end Additionally, employing a sufficient number and size of openings is crucial to prevent distortion of measurement results due to potential extra openings Furthermore, ensuring that the largest openings are adequately sized is necessary to avoid truncating the collected radiation pattern.

NOTE 1 L'alignement optique est critique.

Requirements specific to method B – Mode field diameter by variable aperture in the far field

This annex describes apparatus in addition to the requirements in clause 4.

Figure B.1 illustrates a typical set-up for the measurement by variable aperture in the far field.

Figure B.1 – Variable aperture by far-field measurement set

Position a device with round transmitting apertures of different sizes, like an aperture wheel, at least \(100 \frac{W_0^2}{\lambda}\) away from the specimen to adjust the power extracted from the fiber output far field pattern Generally, these apertures are situated 20 mm apart.

50 mm away from the fibre end.

To reduce sensitivity to fibre end angle, center the apertures relative to the pattern Ensure an adequate number and size of apertures so that measurement results remain unaffected by any additional apertures Additionally, make sure the largest apertures are sufficiently sized to prevent truncation of the collected pattern.

NOTE 1 Optical alignment is critical.

The number and sizes of openings are critical factors affecting the accuracy of this method The optimal configuration may differ depending on the specific fiber model being tested Verification of a particular selection can be enhanced by comparison with Method A, which involves direct exploration in the far field.

B.1.1.1 Prescriptions relatives à l'équipement pour fibre de catégorie B1

The accuracy of the DCM measurement provided by this method relies on the maximum numerical aperture of the measurement setup For B1 category fiber, the error is typically 1% or less with a test setup having a maximum numerical aperture of 0.25 To achieve a lower error or if the sample under test has a DCM less than 8.2 µm, one of the following approaches is necessary: a) use a testing system with a numerical aperture of 0.35 or higher, or b) establish a mapping function to relate the B1 fiber measurement taken with a limited aperture setup to that of a setup with a numerical aperture of 0.35 or greater.

B.1.1.2 Prescriptions relatives à l'équipement pour fibres de catégories B2, B3 et B4

L'ouverture numérique maximale du montage d'essai doit être égale ou supérieure à 0,40 pour des fibres dont les diamốtres du champ de mode sont ộgaux ou supộrieurs à 6 àm.

Utiliser un système optique, tel qu'une paire de lentilles, des miroirs, ou autre dispositif approprié pour collecter toute la lumière transmise à travers l'ouverture, et la coupler au détecteur.

B.1.3 Ensemble détecteur et dispositif électronique de détection des signaux

Utilize a radiation-sensitive detector that operates across the entire wavelength range to be measured and maintains linearity across all encountered intensity levels A typical system may include a germanium or GaInAs photodiode functioning in photovoltaic mode, along with a current preamplifier, while synchronous detection is facilitated by a lock-in amplifier Generally, a computer is recommended for data analysis.

B.2.1 Placer l'échantillon à l’essai, préparé conformément aux prescriptions de 4.2, dans les dispositifs d'alignement des entrées et des sorties, et ajuster correctement sa distance par rapport à l'ensemble à ouvertures.

B.2.2 Régler l'ensemble à ouvertures sur une ouverture de petite taille et ajuster l'alignement latéral champ lointain-ouverture pour une puissance détectée maximale.

B.2.3 Mesurer la puissance détectée pour chacune des ouvertures.

B.2.4 Répéter B.2.3 pour chaque longueur d'onde de mesure spécifiée.

B.2.5 Calculer le DCM suivant l'équation (2) et B.3.

The accuracy of this method is significantly influenced by the number and size of the apertures, which can vary based on the design of the tested fibres To ensure the effectiveness of a specific selection, it is advisable to verify the results through comparison with method A, which involves direct far-field measurements.

B.1.1.1 Equipment requirements for category B1 fibre

The accuracy of MFD measurements is influenced by the maximum numerical aperture of the measurement system For category B1 fibre, an error of 1% or less is achievable with a maximum numerical aperture of 0.25 To reduce error further or for specimens with an MFD less than 8.2 µm, one can either utilize a measurement system with a numerical aperture of 0.35 or higher, or establish a mapping function that correlates measurements from a limited aperture system to those from a system with a numerical aperture of 0.35 or greater.

B.1.1.2 Equipment requirements for category B2, B3, and B4 fibres

The maximum numerical aperture of the measurement set shall be equal to or greater than

0,40 for fibres with MFDs equal to or greater than 6 àm.

Tiêu đề	Mode Field Diameter
Chuyên ngành	Optical Fibres
Thể loại	Standard
Năm xuất bản	2001

Định dạng
Số trang	68
Dung lượng	1,12 MB