CZ33240U1 - Optical train mode structure analyser - Google Patents

Description

Technical field

The technical solution relates to the optical structure analyzer of optical components and solves the encircled flux parameter (EF) for multimode optical fibers (IOC) with a core diameter of 50 to 1000 µm. The advantage of this solution is the parallel evaluation of the EF parameter, the optical beam width, the integral optical power and the purity of the MOV front.

BACKGROUND OF THE INVENTION

The current development of optical fibers and their use is currently focused on data centers and so-called last-mile connections. The MOV can be used for these relatively short optical paths. Due to the dominant mode dispersion in IOC, the development in recent years has focused on still new generations of these fibers in terms of suppression of mode dispersion by optimizing the refractive index profile, resulting in greater bandwidth per unit of length (expressed in MHz / km). Simultaneous use of new generations of fibers from previous generations, as well as using different types of optical sources (LED, LASER, etc.), it is necessary to accurately characterize the optical energy distribution in the IOC, which has a significant impact on the transmission capacity of the system. Characterization is also necessary in order to avoid erroneous and different results in calibration measurements of assembled optical paths from the IOC and to reduce possible service outages associated with a decrease in optical performance.

For the purpose of measuring the distribution of optical energy is used parameter EF (defined according to standards ČSNEN 61280-1-4 ed.2 and ČSN EN 61280-4-1 ed.2). For an accurate evaluation of the EF parameter, it is necessary to make a very accurate measurement of the optical field intensity distribution at the MOV output.

US 7295733 B2 presents a methodology for adjusting the appropriate coupling between a light source (shown by an example of a vertical cavity surface emitting laser (VCSEL) and an MOV using an optical lens) The present solution allows simultaneous alignment of the coupling lens and measurement of the EF parameter. This connection is not concerned with measuring optical power, inspecting the cleanliness of the fiber face or fibers with a large core diameter, and focusing on the fiber face in this embodiment is very inaccurate.

US 9036137 B2 and US 20110096563 A1 disclose an optical signal source having a defined output beam, or EF standardized, with a defined output beam. US 20110096563 A1 also develops the possibility of evaluating an EF parameter using a basic configuration of two lenses and a beam splitter, but without much accuracy or multifunctional use.

Scientific publications currently focus mainly on the measurement of EF for unconventional MOVs (with refractive index change, polymer / plastic fibers), always for a particular fiber type. The difference often lies in the methodology of measuring the EF parameter (near or far field), in the wavelength used (visible region, near infrared 850/1300/1550 nm) and in the actual interpretation of the measured results. However, none of the publications offer a versatile multifunctional method and device to measure the EF Integral Optical Performance and MOV front for a wide range of optical fibers.

A. J. Parker, published in IEEE Transactions on Instrumentation and Measurement, Vol. 44, No. 2, pp. 458 to 460 in April 1995 focuses on the measurement of the field pattern and its distribution for single mode optical fibers, where the main benefit of the article is the effect of confocal confocal

- 1 GB 33240 U1 of the measuring system to the measured value of the field of view. The question of defocussing is also critical for the proposed optical component analyzer and from this point of view the relevant publication is relevant. On the other hand, the principle of confocal microscope differs from the proposed solution, because it allows to measure only one optical mode fibers and also the proposed method measures point-by-point, not at once across the entire optical field on the detector, as the proposed optical structure analyzer component.

R. Billington's contribution to the Effective Area of Optical Fibers - Definition and Measurement Techniques, published as a 1999 publication by the NPL Center for Optical and Environmental Metrology, further develops the methodology for measuring single-mode optical fibers and discusses differences in near and far field measurements. The methodology itself is identical to the article by A.J. Parker and shows the same drawbacks compared to the present solution.

K. Miyagi et al. in the article Measurements of Mode Field Diameter and Effective Area of Photonic Crystal Fibers by Far-Field Scanning Technique published in OPT REV, Vol. 17, pp. 388, 2010 published a measurement of microstructured optical fibers using a remote field method and determined a correction factor for calculating the field trace. The correction factor methodology is an interesting benefit, but the methodology does not allow a good evaluation of the EF parameter due to the use of remote field measurements or fiber measurements with larger core diameters.

F. Susanto et al. in the article Encircled Flux-based Optimized Simple Launch Condition for Standardization of Multimode Polymer Optical Wavavuide Evaluations published in Opt. Express 18, pp. 23554 to 23561, 2010 dealt with polymer optical fibers and EF parameter requirements for optimum optical signal source. The publication deals with the measurement of EF parameters using the near-field method and CCD camera. Illumination, focus verification and fiber front cleanliness are not addressed, which brings a significant error to the measurement.

M. Kagami et al. in the article Encircled Angular Flux Representation of Modal Power Distribution and Its Behavior in a Step Index Multimode Fiber published in Journal of Lightwave Technology, Vol. 34, No. 3, pp. 943 to 951, 2016 details the measurement of the EF parameter for the MOV with a step change in the refractive index for the plastic MOV, which represents only one MOV group. Also, the published methodology is based on remote field measurements, which means less measurement accuracy and does not match EF measurements to the above standards.

So far known solutions deal with eg EF measurement, evaluation of integral power or purity of the front of the MOV, but it is always only individual applications, not a complex solution that would allow to measure simultaneously the same parameter EF, integral optical power, evaluate optical beam parameters and inspect the purity of the MOV front. In addition, the available solutions are only designed for specific IOCs with a given core diameter. None of the known solutions also utilizes a homogeneous full-area backlighting of the measured IOC. This is one of the reasons why the known solutions do not offer a way to achieve the evaluation of the EF parameter, the measurement of the optical power and the inspection of the cleanliness of the fiber front in parallel. The use of fibers of different core diameters, which would also apply to plastic optical fibers, is also not addressed in the prior art.

The essence of the technical solution

The aforementioned drawbacks are overcome by the optical fiber mode analyzer of the present invention, which comes with a completely new approach when designing a homogeneous full-area backlight of the analyzed optical fiber. The present analyzer is a complex and multifunctional device allowing measurement of several parameters, in addition with a high variability of analyzable MOVs.

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The optical fiber mode analyzer comprises a first holder for fastening the output face of the optical fiber being analyzed. The position and construction of this holder determine the position of the exit face of the analyzed optical fiber. The analyzer further comprises an optical beam splitter, a first lens disposed between the first holder and the optical beam splitter, a illuminating optical fiber having an output face attached to the second holder and facing the light source with its input face and a second lens disposed between the optical beam splitter. and an output face of the illuminating optical fiber. Both the lenses, the output face of the analyzed optical fiber and the output face of the illuminating optical fiber are positioned in a position in which they share a common optical axis, and the optical beam splitter is positioned such that it intersects the optical axis. At least one of the holders is adjustable. The analyzer also includes a detector positioned such that when the optical beam strikes the optical beam splitter in a direction away from the first lens parallel to the optical axis, the portion of the beam deflected from the original direction is directed to the detector. The essence of the analyzer according to the present invention is that the position of the exit face of the analyzed optical fiber is adjustable to the focal plane of the first lens and that the second lens is bi-convex with a numerical aperture greater than the numerical aperture of the illuminating optical fiber. the diameter of the optical beam emerging from the illuminating optical fiber at the location of the second lens.

In a preferred embodiment, the first lens is aspherical.

It is preferred that the illuminating optical fiber is a fiber with a homogeneous distribution of intensity in the radial direction.

Preferably, the first holder and the second holder are adjustable with at least three degrees of freedom.

In a preferred embodiment, the parameters of the illuminating optical fiber and the lenses and their geometric configuration are such that the illuminating optical fiber together with the second lens and then the first lens form an optical beam with a larger field trace than the diameter of the shells analyzed optical fibers for which the analyzer is designed.

Also preferred is an embodiment in which the parameters of the illuminating light source, the parameters of the illuminating optical fiber and the mutual geometric arrangement of the illuminating light source and the illuminating optical fiber are such that the diameter of the visual field bounded from the illuminating light source to the illuminating optical fiber is at least 36 µm.

By using the presented solution it is possible to ensure measurement of the EF parameter, integral optical power, evaluation of optical beam parameters and inspection of the purity of the MOV front. This is made possible by the near-field measurement of the tested MOV in combination with the MOV illumination of the front of the MOV homogeneously distributed optical beam. By properly adjusting the optical elements, a wide range of analizable MOVs can be achieved, with a core diameter in the range of 50 µm to 1000 µm.

Clarification of drawings

Figure 1 is a diagram of an optical fiber mode analyzer according to the present invention.

FIG. 2 is a diagram of the same analyzer with the optical fiber being analyzed.

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Examples of technical solutions

Fig. 1 shows an exemplary embodiment of an optical fiber mode analyzer according to the present invention; in Fig. 2, the same analyzer is already inserted with the analyzed optical fiber for better understanding. The analyzer is specifically designed to analyze many optical fibers or analyzed optical fiber 1. is typically many modes. However, it can also be used for some single-fiber measurements. The analyzed optical fiber 1 is preceded by a light source 10 for the analyzed optical fiber 1, which can either be firmly connected to it or located some distance from the input face of the analyzed optical fiber 1, but always so that light from the light source 10 the analyzed optical fiber 1 hit the input face of the analyzed optical fiber L

The figures in Figures 1 and 2 are only schematic, not to scale, and even the ratios of individual distances and sizes may be different in different embodiments. At the same time, other elements such as additional lenses or diffractive elements can be added. It will be apparent to those skilled in the art that the schemes shown in Figures 1 and 2 and the following description of preferred embodiments can be readily used as a basis for modifying or designing other optical devices serving the same purpose as the present invention. protection as set out in the attached protection claims.

The fibers to be analyzed for which the analyzer is specifically designed are typically multimode, most often with core diameters from 50 µm to 1000 µm.

It can be seen from Fig. 1 that the optical fiber mode analyzer comprises a first holder 6 for fastening the output face of the analyzed optical fiber L The position and construction of this holder determine the position of the L1 location for the output face of the analyzed optical fiber. is defined by fixing the outlet end of the analyzed optical fiber 1 to the first holder 6, and can preferably be moved by positioning the first holder 6. The analyzer further comprises an optical beam splitter 5, a first lens 3 disposed between the first holder 6 and an optical beam splitter 5, an illuminating optical fiber 2, the output face of which is attached to the second holder 7 and which faces the light source 11 with its input face, and a second lens 4 disposed between the beam splitter 5 and the light output face The illumination light source 11 may be connected to the illumination optical fiber 2, but this is not a requirement, it may be located at a non-zero distance therefrom, but always so that light from the illumination light source 11 falls on the entrance face of the illumination light source. The two lenses 3, 4, instead of L1 for the output face of the optical fiber 1 to be analyzed, and the output face of the illumination optical fiber 2 are both positioned in a position in which they share a common optical axis 9. The optical beam splitter 5 is positioned such that the optical axis 9 intersects. At least one of the holders 6, 7 is adjustable, which is needed, inter alia, to adjust the relative position of the output faces of the illumination fiber 2 and the analyzed optical fiber 1 in a direction perpendicular to the optical axis. This can also be used to position these output faces in a direction parallel to the optical axis. The analyzer also includes a detector 8 disposed so that when the optical beam splitter 5 strikes the optical beam in a direction away from the first lens 3 parallel to the optical axis 9, the portion of the optical beam deflected by the divider 5 from the original direction is directed to the detector 8 by falls on its sensitive area. The sensitive surface of the detector 8 is thus located in the path of the optical beam deviated by the divider 5 from the original direction parallel to the optical axis 9.

It is essential that the position of the position L1 for the output face of the analyzed optical fiber 7 is adjustable to the focal plane of the first lens 3, which can be achieved either by moving the first holder 6 or by moving the first lens 3. wherein the second lens 4 is bi-convex with a numerical aperture greater than the numerical aperture of the illuminating optical fiber 2, the second lens 4 having a diameter exceeding the diameter of the optical beam coming from the illuminating optical fiber 2 at the location of the second lens

-4GB 33240 U1 lens 4 placed. The diameter of the optical beam coming from the illuminating optical fiber 2 at the location of the second lens 4 is determined by the parameters of the illuminating optical fiber 2, the parameters of the illuminating light source 11 and the relative position of the output face of the illuminating optical fiber 2 and the second lens 4. preferably adjustable.

Due to this arrangement and due to its above-mentioned parameters, the second lens 4 adjusts the optical beam from the illuminating optical fiber 2 so that the optical intensity at the output of this second lens 4 reaches a homogeneous distribution while ensuring sufficient illumination of the front face of the analyzed optical fiber 1. . Illumination of the front of the analyzed optical fiber 1 leads to a distinction of the interface of the core, the sheath and the polymer protection, which, given the given dimensions, can infer the magnification of the first lens 3, thereby enabling calibration of the system. purity of the optical fiber to be analyzed

Typically, the second lens 4 also has a diameter of at least 1 times greater than the core diameter of the analyzed optical fibers for which the analyzer is intended

The lenses 3, 4, holders 6, 7 of the optical beam splitter 5 and the detector 8 are fixed during the analysis of the optical fiber 1, e.g. to the optical bench, but at least some of these elements can be positionally adjustable. for centering on the common optical axis 9, tuning the mutual distances a, b, c, d, e. The first distance a between the front point 1.1 of the optical fiber 1 to be analyzed and the first lens 3 a second distance b between the first lens 3 and the optical splitter 5 The third distance c between the optical beam splitter 5 and the second lens 4 and the fourth distance d between the second lens 4 and the output face of the illuminating optical fiber 2 serves to tune the second lens 4 with respect to to the illuminating optical fiber 2 so as to provide sufficient illumination Adjusting the front of the analyzed optical fiber E Setting the fifth distance e between the beam splitter 5 and the detector 8 then allows optimal illumination of the detector 8 so that the field trace extends over the entire surface of the detector 8. In minimal configuration of the device. However, the distances a, b, c, d, e mentioned above need not be permanently adjustable, they can be fixed or fixed only some of them.

Preferably, the first lens 3 is aspherical. Due to this and thanks to the positioning of the output face of the analyzed optical fiber 7 in the focal plane of this first lens 3, the measured parameters of the analyzed optical fiber 1 are precisely evaluated. At the same time

Preferably, the illuminating optical fiber 2 is a fiber with a homogeneous distribution of intensity in the radial direction. One possible example is a multimode optical fiber with a 50 or 62.5 µm refractive index profile.

In a preferred embodiment, the first holder 6 and the second holder 7 are adjustable with at least three degrees of freedom, typically backwards to degrees of freedom. The holders are typically adjustable in degree of freedom in the direction of the optical axis 9, in two directions perpendicular thereto and with the possibility of angular rotation about two different axes. In the case of less than 5 degrees of freedom, the directions of movement selected from the above five. The holders may, but are also equipped with movement mechanisms other than those described above.

It is preferred that the parameters of the illuminating optical fiber 2 and the lenses 3, 4 and their geometric configuration are such that the illuminating optical fiber 2, together with the second lens 4 and subsequently the first lens 3, forms an optical beam at the exit point E1 of the analyzed optical fiber 1. with a larger optical field trace than the diameter of the shells

The analyzed optical fibers for which the analyzer is intended. This leads to accurate calibration and determination of the overall system magnification for accurate evaluation of EF parameter.

It is also preferred that the parameters of the light source 11, the light source fiber 2 and the geometrical arrangement of the light source 11 and the light source 2 are such that the diameter of the field of view connected from the light source 11 to the light source 2 is at least 36. pm, using the usual definition of the field trace diameter to decrease the optical power to 1 / e ^{2 of the} maximum optical power, taking into account the Gaussian or near Gaussian optical power distribution. This preferred arrangement contributes to a more homogeneous distribution of the field strength of the illuminated optical fiber E

The illuminating optical fiber 2 is typically multimode with a core diameter equal to or greater than 50 µm.

The principle of the present solution lies in several steps. In the first step, the analyzed optical fiber 1 is inserted into the optical fiber mode analyzer and tuned to the optical axis 9. Then the signal from the light source 11 is applied to the light fiber 2. According to the image from the detector 8, the first distance and / or the second distance b of the first lens 3 in the direction along the optical axis and the analyzed optical fiber 1 is thus tuned to the focus of the first lens 3. According to the size of the analyzed optical fiber 1, which usually has a diameter of 50 to 1000 µm, so that the whole face of the analyzed optical fiber is illuminated EV This step can also identify contamination of the face of the analyzed optical fiber E The device is calibrated, the whole system magnification is determined to accurately evaluate the EF parameter. Thereafter, the illumination optical signal in the illumination light source 11 is switched off and the signal from the light source 10 for the analyzed optical fiber is released to the analyzed optical fiber 1. The detector 8 senses the field pattern distribution and mode field, respectively EF parameter. From the measured field field trace, the integral optical power can be derived (after attenuation correction from beam splitter 5).

The main advantage of the present solution lies in the fast and extremely precise alignment of the analyzed optical fiber 1, or more precisely its output face, to the focal plane of the first lens 3 by means of counter-illumination with an optical signal with homogeneous optical intensity distribution coming from the illuminating optical fiber This results in a much more accurate evaluation of the EF parameter measured in the near field. Furthermore, this allows for additional functionalities such as measurement of integral optical power, measurement of optical beam width, and evaluation of the cleanliness of the analyzed optical fiber E

The present solution enables to achieve high accuracy of EF parameter for analyzed optical fiber 1.

In the most preferred embodiment of the present invention, the aspherical first lens 3 and the second bi-convex lens 4 are combined, realizing the detector 8 using a CCD / CMOS element and precisely adjusting all components so that the output face of the analyzed optical fiber 7 is precisely tuned to the focal length with respect to the first lens 3 and at the same time the counter-beam is slightly defocussed by passing through the first lens 3 so that the cleanliness of the output face of the analyzed optical fiber 7 and its design parameters can be evaluated. Also, in the most preferred embodiment, the entire ambient light enclosure configuration is substantially suppressed by the noise level. The measured EF and beam profile parameters can be measured to the nearest tenth of a micrometer to ensure sufficient usability of the method.

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Industrial applicability

The invention finds wide application in evaluation of multimode optical fibers and signal sources, where it is necessary to define the distribution of the visual field according to the standard. This is critical mainly in multimode optical networks, mainly in the data center area, where it is necessary to guarantee insertion losses for multimode optical fiber connections.

PROTECTION REQUIREMENTS

Claims (7)

An optical fiber mode analyzer comprising a first holder (6) for attaching an output face of the analyzed optical fiber (1), wherein the position and construction of the holder determine the position (1.1) for the output face of the analyzed optical fiber (1), and a splitter (5) an optical beam, a first lens (3) disposed between the first holder (6) and the optical beam splitter (5), an illuminating optical fiber (2) whose output face is attached to the second holder (7) and which is its input face facing the illumination light source (11), and a second lens (4) located between the optical beam splitter (5) and the output face of the illumination optical fiber (2), both lenses (3, 4) instead of (1.1) for the output face of the analyzed the optical fiber (1) and the output face of the illuminating optical fiber (2) are both positioned in a position in which they share a common optical axis (9) and a splitter (5) The beam is positioned such that the optical axis (9) intersects, at least one of the holders (6, 7) being adjustable, the analyzer also comprising a detector (8) positioned so that when the optical beam strikes the optical beam splitter (5) in the direction away from the first lens (3) parallel to the optical axis (9), the part of the optical beam deflected by the divider (5) from the original direction is directed to the detector (8), characterized in (1) is adjustable to the focal plane of the first lens (3), and that the second lens (4) is bi-convex with a numerical aperture greater than the numerical aperture of the illuminating optical fiber (2), the second lens (4) having a diameter exceeding the diameter an optical beam coming from the illuminating optical fiber (2) at the location of the second lens (4). Analyzer according to claim 1, characterized in that the first lens (3) is aspherical. Analyzer according to claim 1 or 2, characterized in that the illuminating optical fiber (2) is a fiber with a homogeneous distribution of intensity in the radial direction. Analyzer according to any one of claims 1 to 3, characterized in that the first holder (6) and the second holder (7) are adjustable with at least three degrees of freedom. Analyzer according to any one of claims 1 to 4, characterized in that the parameters of the illuminating optical fiber (2) and the lenses (3, 4) and their geometrical arrangement relative to each other are such that the illuminating optical fiber (2) together with the second lens (3). 4) and thereafter the first lens (3) forms, at a point (1.1) for the output face of the analyzed optical fiber (1), an optical beam with a larger field field trace than the diameter of the optical fiber sheaths for which the analyzer is intended. Analyzer according to any one of claims 1 to 5, characterized in that the parameters of the illuminating light source (11), the parameters of the illuminating optical fiber (2) and the mutual geometric arrangement of the illuminating light source (11) and the illuminating optical fiber (2) Are such that the diameter of the field of view of the video field coupled from the illuminating light source (11) to the illuminating optical fiber (2) is at least 36 µm.