CN118583070A - Optical fiber mode field diameter measuring device and method based on far-field aperture method - Google Patents
Optical fiber mode field diameter measuring device and method based on far-field aperture method Download PDFInfo
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Abstract
The invention discloses a device and a method for measuring the diameter of an optical fiber mode field based on a far-field aperture method, which belong to the technical field of optical communication, wherein the device comprises a small aperture diaphragm, a focusing module and an optical power meter; the light emitted by the output end of the optical fiber to be measured is partially blocked by the small-hole diaphragm and then is incident to the focusing module, and the optical power meter is positioned on the focal plane of the focusing module and used for measuring the optical power at the focal plane. The maximum power received by the ambient light power and the initial position of the transmitting end are recorded by the power meter; the radius of the diaphragm is regulated to make the change of the optical power more remarkable when the diaphragm moves; and moving the diaphragm to the position closest to the convex lens, gradually moving the diaphragm to the emitting end, recording a series of optical power readings and corresponding positions, and calculating the diameter of the optical fiber mode field by combining the positions of the aperture diaphragm.
Description
Technical Field
The invention belongs to the technical field of optical communication, and relates to an optical fiber mode field diameter measuring device and method based on a far-field aperture method.
Background
The single-mode fiber has large communication capacity, is convenient to lay and transport, and has great effect in optical fiber communication. An important parameter of a single-mode fiber, the mode field diameter, can be used to describe the maximum diameter of the total reflection cross-section of light propagating in the fiber, as well as the concentration of light energy transmitted by the fiber. The mode field diameter is different from the core diameter, and for a uniform single-mode fiber, the fundamental mode field strength is approximately gaussian across the fiber, and the width corresponding to the maximum of the field strength profile in the fiber is generally defined as the mode field diameter. Mode field diameter is a very important parameter in optical fiber communications, from which many important properties of the optical fiber, such as coupling efficiency, bending losses, etc., can be derived. Therefore, accurate measurement of the mode field diameter is of great significance for improving engineering quality of an optical fiber communication system and the like. There are various methods for measuring the mode field diameter, such as: 1. in the patent number CN115824071A, the invention patent of the device and the method for measuring the effective diameter of the fiber core of the optical fiber provides a device and a method for measuring the effective diameter of the fiber core of the optical fiber, which can realize the test of the mode field diameter and the numerical aperture and can be suitable for multiple-size and multiple-type optical fibers; 2. in the invention patent with the publication number of CN115373080A, a high-definition hollow fiber resonant cavity with high mode field coupling efficiency and a construction method thereof are provided, and the detection performance of the whole hollow fiber resonant cavity is improved.
However, the following technical difficulties exist in the current measurement of the mode field diameter of the optical fiber: 1. the manual measurement mode is complex to operate and difficult to learn, and once the operation is careless, heavy errors are easy to occur; 2. the accuracy of the automatic measurement mode is poor, and systematic errors which are difficult to eliminate easily occur.
Disclosure of Invention
Aiming at the defects and improvement demands of the prior art, the invention provides an optical fiber mode field diameter measuring device and method based on a far-field aperture method, which aim to measure the mode field diameter of an optical fiber with high precision in a concise and easily understood mode and enable a user to detect and exclude most of system errors.
To achieve the above object, according to one aspect of the present invention, there is provided an optical fiber mode field diameter measuring apparatus comprising: the device comprises a small aperture diaphragm, a focusing module and an optical power meter; the light emitted by the output end of the optical fiber to be measured is partially blocked by the aperture diaphragm and then enters the focusing module, and the optical power meter is positioned on the focal plane of the focusing module and is used for measuring the optical power of a series of focal planes in the process that the aperture diaphragm moves from the nearest position of the focusing module to the emitting end; and calculating the diameter of the optical fiber mode field by combining the positions of the aperture diaphragms.
Further, the output end of the optical fiber to be measured, the center of the aperture diaphragm and the center of the focusing module are on the same horizontal straight line.
Further, the focusing module is a convex lens.
The invention also provides a fiber mode field diameter measuring method based on the fiber mode field diameter measuring device, which comprises the following steps:
Coupling light emitted by a light source into the optical fiber to be tested, outputting the light through the output end of the optical fiber to be tested, and then irradiating the light to the aperture diaphragm, and adjusting the position of the output end of the optical fiber to be tested, so that the output end of the optical fiber to be tested, the center of the aperture diaphragm and the center of the focusing module are in the same horizontal straight line;
The aperture diaphragm is moved to the nearest position from the focusing module, then the aperture diaphragm is gradually moved towards the emitting end, the optical power readings P i at a series of focal planes and the corresponding positions z i are recorded, and the optical fiber mode field diameter omega G is calculated.
Further, the method also comprises the following steps:
the aperture diaphragm is removed, and the power P e of the ambient light when the light source is turned off and the maximum power P max received by the power meter when the light source is turned on are recorded.
Further, the fiber mode field diameter ω G is determined by:
Wherein lambda is the wavelength of light emitted by the light source, k is the slope of a fitted linear function, which uses sin 2θi as an abscissa value, For the ordinate value, the fiber aperture angle sin θ i is expressed as:
The optical power P αi of the aperture stop is determined by:
Pαi＝Pi-Pe
Where P e is the ambient light power, P i is the light power reading at the focal plane, z i is the position of the aperture stop, P max is the maximum power received by the light power meter when the aperture stop is removed and the light source is turned on, and R is the radius of the aperture stop.
It should be noted that, the system error of the present invention mainly includes: 1.Is approximated by the actual formula ofWill be in calculationThe actual result is larger when the actual result is approximately sin theta; 2. the center of the diaphragm is deviated from the center of the light spot, and the actual result is smaller; 3. the actual result is small because the light cannot be coupled 1:1. However, the precision of the existing instrument is enough to control the error within the range of the requirements of the optical engineering industry, and the actual application cannot be affected visually.
In general, through the above technical solutions conceived by the present invention, the following beneficial effects can be obtained:
(1) Aiming at the problems that a manual measurement mode in the field of fiber mode field diameter measurement is complex to operate and difficult to learn, the invention adopts a simple and easily understood mode to construct an experimental instrument, and the related optical devices are all common laboratory equipment, and the equipment has the characteristics of simple structure, low cost and easy acquisition, and is easy to learn and master by a user.
(2) Aiming at the problem that a manual measurement mode in the field of fiber mode field diameter measurement is easy to cause heavy errors once being carelessly operated, the invention introduces experimental inspection in the measurement process, and constructs a method which is easy to detect and remove most experimental errors, and specifically comprises the following steps: the diaphragm is moved away, the light blocking cloth is put down, and the power P e of the ambient light when the laser transmitter is turned off and the maximum power P max received by the power meter when the laser transmitter is turned on are recorded; then, the radius of the diaphragm is adjusted to be a proper size R, so that when the diaphragm moves in a relatively large range, the change of the optical power is more remarkable, and the aperture diaphragm always shields part of laser in the moving process, so that P a<Pmax is ensured; next, the adjusted diaphragm is moved to the nearest position to the convex lens, then gradually moved toward the emitting end, a series of optical power readings P i and corresponding positions z i are recorded, and a test value ω G0 of the optical fiber mode field diameter is calculated. The method can effectively find out common errors in the instrument construction process, and is beneficial to preventing the condition that an experimenter operates carelessly.
(3) Aiming at the problem of poor precision of an automatic measurement mode in the field of fiber mode field diameter measurement, the invention constructs a method for measuring the fiber mode field diameter with high precision.
Drawings
FIG. 1 is a schematic diagram of a fiber mode field diameter measurement device based on a far field aperture method according to an embodiment of the present invention;
Fig. 2 is a schematic flow chart of a method for measuring the diameter of an optical fiber mode field based on a far-field aperture method.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention. In addition, the technical features of the embodiments of the present invention described below may be combined with each other as long as they do not collide with each other.
The invention provides an optical fiber mode field diameter measuring device, as shown in fig. 1, comprising: the device comprises a small aperture diaphragm, a focusing module and an optical power meter; the light emitted by the output end of the optical fiber to be measured is partially blocked by the aperture diaphragm and then enters the focusing module, and the optical power meter is positioned on the focal plane of the focusing module and is used for measuring the optical power of a series of focal planes in the process that the aperture diaphragm moves from the nearest position of the focusing module to the emitting end; and calculating the diameter of the optical fiber mode field by combining the positions of the aperture diaphragms.
Specifically, the output end of the optical fiber to be measured, the center of the aperture diaphragm and the center of the focusing module are on the same horizontal straight line.
Specifically, the focusing module is a convex lens.
The invention also provides a fiber mode field diameter measuring method based on the fiber mode field diameter measuring device, as shown in figure 2, comprising the following steps:
Coupling light emitted by a light source into the optical fiber to be tested, outputting the light through the output end of the optical fiber to be tested, and then irradiating the light to the aperture diaphragm, and adjusting the position of the output end of the optical fiber to be tested, so that the output end of the optical fiber to be tested, the center of the aperture diaphragm and the center of the focusing module are in the same horizontal straight line;
The aperture diaphragm is moved to the nearest position from the focusing module, then the aperture diaphragm is gradually moved towards the emitting end, the optical power readings P i at a series of focal planes and the corresponding positions z i are recorded, and the optical fiber mode field diameter omega G is calculated.
Further, the method also comprises the following steps:
the aperture diaphragm is removed, and the power P e of the ambient light when the light source is turned off and the maximum power P max received by the power meter when the light source is turned on are recorded.
Further, the fiber mode field diameter ω G is determined by:
Wherein lambda is the wavelength of light emitted by the light source, k is the slope of a fitted linear function, which uses sin 2θi as an abscissa value, For the ordinate value, the fiber aperture angle sin θ i is expressed as:
The optical power P αi of the aperture stop is determined by:
Pαi＝Pi-Pe
Where P e is the ambient light power, P i is the light power reading at the focal plane, z i is the position of the aperture stop, P max is the maximum power received by the light power meter when the aperture stop is removed and the light source is turned on, and R is the radius of the aperture stop.
In order to implement the above method, the present invention gives specific examples:
example 1
A fiber optic mode field diameter measurement device, comprising: optical bench, experimental optical power measuring instrument, electric optical bench and optical focusing system produced by Realight company, optical fiber (ω G = 4.600 μm) for test, 650nm 10nW grade He-Ne laser transmitter, 1310/1550nm1mW grade laser transmitter, aperture diaphragm, optical fiber jumper and light shielding cover cloth. The instrument is built according to the following steps:
S1, constructing an optical path so that the emergent end of the coupling optical fiber, the center of the aperture diaphragm and the center of the optical lens are on the same horizontal straight line as much as possible.
S2, placing the optical fiber emergent end on the stabilizing frame, enabling the end face of the optical fiber emergent end to be flush with the edge of the stabilizing frame, and adjusting the stabilizing frame to a proper height. And (3) adjusting the aperture radius of the aperture diaphragm to be minimum, and adjusting the height of the diaphragm to enable the center of the light spot to be just hit at the center of the diaphragm. Likewise, the convex lens height is adjusted so that the spot center and the convex lens center substantially coincide.
S3, the receiving end face of the sliding power meter is positioned at the focus of the convex lens, a 650nm laser transmitter of the power meter is turned on, the radius of a small aperture diaphragm is adjusted to be maximum, the height of the receiving end of the power meter and the front, back, left and right positions are adjusted, and the power displayed by the power meter reaches the maximum value.
The experiment was performed according to the following steps:
T1, removing the diaphragm, placing the light blocking cloth, recording the power P e of the ambient light when the laser transmitter is turned off and the maximum power P max received by the power meter when the laser transmitter is turned on, and recording the initial position z 0 of the transmitting end; then, the radius of the diaphragm is adjusted to be a proper size R, so that when the diaphragm moves in a relatively large range, the change of the optical power is more remarkable, and the aperture diaphragm always shields part of laser in the moving process, so that P a<Pmax is ensured.
And T2, then moving the adjusted diaphragm to the position closest to the convex lens, gradually moving the diaphragm to the transmitting end, moving the diaphragm by 3mm each time, switching the wavelength of the laser transmitter and the receiving wavelength of the power meter, recording a series of optical power readings P i and the corresponding position z i, and calculating a test value omega G0 of the optical fiber mode field diameter, wherein the calculation method is as follows: the optical power P αi passing through the aperture diaphragm measured in each experiment and the optical fiber aperture angle sin theta i measured in each experiment are calculatedAnd sin 2θi, and taking sin 2θi as an abscissa value,Constructing a scatter diagram for a longitudinal coordinate value, fitting by using a linear function, marking the slope as k and marking the intercept as b; optical fiber mode field diameterThe optical power P αi＝Pi-Pe measured through the aperture stop per experiment, where P e is the ambient optical power measured in T1; the aperture angle of the optical fiber measured by each experiment
Wherein, the optical experiment frame uses electronic experiment frame, and the aperture diaphragm uses electronic aperture diaphragm to reduce the error. The power of the 650nm He-Ne laser transmitter is greater than 10nW, and the power of the 1310/1550nm laser transmitter is mW. In addition, in order to ensure far field conditions, the distance between the aperture diaphragm and the transmitting end is ensured to be more than 10cm in the measuring process.
The embodiment has simple thought, simple and understandable device and convenient teaching and explanation; the whole operation is easy, and the operation of students is convenient; the device is easy to purchase, relatively low in cost and not easy to damage, and is suitable for being used as a teaching aid with consumable properties.
It will be readily appreciated by those skilled in the art that the foregoing description is merely a preferred embodiment of the invention and is not intended to limit the invention, but any modifications, equivalents, improvements or alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the invention.
Claims (6)
1. An optical fiber mode field diameter measuring device based on far field aperture method, which is characterized by comprising: the output end of the optical fiber to be measured, the center of the aperture diaphragm and the center of the focusing module are positioned on the same horizontal straight line; the light emitted by the output end of the optical fiber to be measured is partially blocked by the aperture diaphragm and then enters the focusing module, and the optical power meter is positioned on the focal plane of the focusing module and is used for measuring the optical power of a series of focal planes in the process that the aperture diaphragm moves from the nearest position of the focusing module to the emitting end; and calculating the diameter of the optical fiber mode field by combining the positions of the aperture diaphragms.
2. The fiber optic mode field diameter measurement device of claim 1, wherein the focusing module is a convex lens.
3. The fiber mode field diameter measurement device of claim 1, wherein the fiber mode field diameter ω G is determined by:
Wherein lambda is the wavelength of light emitted by the output end of the optical fiber to be measured, k is the slope of a fitted primary function, the primary function takes sin 2θi as an abscissa value, For the ordinate value, the fiber aperture angle sin θ i is expressed as:
The optical power P αi of the aperture stop is determined by:
Pαi＝Pi-Pe
Where P e is the ambient light power, P i is the light power reading at the focal plane, z i is the position of the aperture stop, P max is the maximum power received by the light power meter when the aperture stop is removed and the light source is turned on, and R is the radius of the aperture stop.
4. A method of measuring a fiber mode field diameter based on the fiber mode field diameter measuring device according to any one of claims 1 to 3, comprising the steps of:
Coupling light emitted by a light source into the optical fiber to be tested, outputting the light through the output end of the optical fiber to be tested, and then irradiating the light to the aperture diaphragm, and adjusting the position of the output end of the optical fiber to be tested, so that the output end of the optical fiber to be tested, the center of the aperture diaphragm and the center of the focusing module are in the same horizontal straight line;
The aperture diaphragm is moved to the nearest position from the focusing module, then the aperture diaphragm is gradually moved towards the emitting end, the optical power readings P i at a series of focal planes and the corresponding positions z i are recorded, and the optical fiber mode field diameter omega G is calculated.
5. The method of measuring a mode field diameter of an optical fiber according to claim 4, further comprising the steps of:
the aperture diaphragm is removed, and the power P e of the ambient light when the light source is turned off and the maximum power P max received by the power meter when the light source is turned on are recorded.
6. The method of claim 4, wherein the fiber mode field diameter ω G is determined by:
Wherein lambda is the wavelength of light emitted by the light source, k is the slope of a fitted linear function, which uses sin 2θi as an abscissa value, For the ordinate value, the fiber aperture angle sin θ i is expressed as:
The optical power P αi of the aperture stop is determined by:
Pαi＝Pi-Pe
Wherein, P e is the ambient light power, P max is the maximum power received by the light power meter when the aperture diaphragm is moved away and the light source is turned on, and R is the radius of the aperture diaphragm.
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| CN202410655053.0A CN118583070A (en) | 2024-05-24 | 2024-05-24 | Optical fiber mode field diameter measuring device and method based on far-field aperture method |
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| CN202410655053.0A CN118583070A (en) | 2024-05-24 | 2024-05-24 | Optical fiber mode field diameter measuring device and method based on far-field aperture method |
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